The plague disease, originally thought to be caused by Yersinia pestis

Yersinia pestis

Yersinia pestis is a Gram-negative rod-shaped bacterium. It is a facultative anaerobe that can infect humans and other animals....

, is enzootic

Enzootic

Enzootic is the non-human equivalent of endemic and means, in a broad sense, "belonging to" or "native to", "characteristic of", or "prevalent in" a particular geography, race, field, area, or environment; native to an area or scope....

 (commonly present) in populations of ground rodent

Rodent

Rodentia is an order of mammals also known as rodents, characterised by two continuously growing incisors in the upper and lower jaws which must be kept short by gnawing....

s in Central Asia

Central Asia

Central Asia is a core region of the Asian continent from the Caspian Sea in the west, China in the east, Afghanistan in the south, and Russia in the north...

. A recent publication in Nature Genetics, reported the origin of the plague bacillus to be in China. An older theory places the first cases in the steppe

Steppe

In physical geography, steppe is an ecoregion, in the montane grasslands and shrublands and temperate grasslands, savannas, and shrublands biomes, characterized by grassland plains without trees apart from those near rivers and lakes...

s of Central Asia, although some speculate that it originated around northern India

North India

North India, known natively as Uttar Bhārat or Shumālī Hindustān , is a loosely defined region in the northern part of India. The exact meaning of the term varies by usage...

, and others, such as the historian Michael W. Dols, argue that the historical evidence concerning epidemics in the Mediterranean and specifically the Plague of Justinian

Plague of Justinian

The Plague of Justinian was a pandemic that afflicted the Eastern Roman Empire , including its capital Constantinople, in 541–542 AD. It was one of the greatest plagues in history. The most commonly accepted cause of the pandemic is bubonic plague, which later became infamous for either causing or...

 point to a probability that the Black Death originated in Africa and spread to Central Asia, where it then became entrenched among the rodent population. Nevertheless, from Central Asia it was carried east and west along the Silk Road

Silk Road

The Silk Road or Silk Route refers to a historical network of interlinking trade routes across the Afro-Eurasian landmass that connected East, South, and Western Asia with the Mediterranean and European world, as well as parts of North and East Africa...

, by Mongol

Mongols

Mongols ) are a Central-East Asian ethnic group that lives mainly in the countries of Mongolia, China, and Russia. In China, ethnic Mongols can be found mainly in the central north region of China such as Inner Mongolia...

 armies and traders making use of the opportunities of free passage within the Mongol Empire

Mongol Empire

The Mongol Empire , initially named as Greater Mongol State was a great empire during the 13th and 14th centuries...

 offered by the Pax Mongolica

Pax Mongolica

The Pax Mongolica is a Latin phrase meaning "Mongol Peace" coined by Western scholars to describe the stabilizing effects of the conquests of the Mongol Empire on the social, cultural, and economic life of the inhabitants of the vast Eurasian territory that the Mongols conquered in the 13th and...

. It was reportedly first introduced to Europe at the trading city of Caffa in the Crimea

Crimea

Crimea , or the Autonomous Republic of Crimea , is a sub-national unit, an autonomous republic, of Ukraine. It is located on the northern coast of the Black Sea, occupying a peninsula of the same name...

 in 1347. After a protracted siege, during which the Mongol army under Jani Beg

Jani Beg

Jani Beg was a khan of the Golden Horde from 1342 to 1357, succeeding his father Uzbeg Khan.After putting two of his brothers to death, Jani Beg crowned himself in Saray-Jük. He is known to have actively interfered in the affairs of Russian principalities and of Lithuania...

 was suffering the disease, they catapulted the infected corpses over the city walls to infect the inhabitants. The Genoese

Republic of Genoa

The Most Serene Republic of Genoa |Ligurian]]: Repúbrica de Zêna) was an independent state from 1005 to 1797 in Liguria on the northwestern Italian coast, as well as Corsica from 1347 to 1768, and numerous other territories throughout the Mediterranean....

 traders fled, bringing the plague by ship into Sicily and the south of Europe, whence it spread. Whether or not this hypothesis is accurate, it is clear that several preexisting conditions such as war

War

War is a state of organized, armed, and often prolonged conflict carried on between states, nations, or other parties typified by extreme aggression, social disruption, and usually high mortality. War should be understood as an actual, intentional and widespread armed conflict between political...

, famine

Famine

A famine is a widespread scarcity of food, caused by several factors including crop failure, overpopulation, or government policies. This phenomenon is usually accompanied or followed by regional malnutrition, starvation, epidemic, and increased mortality. Every continent in the world has...

, and weather contributed to the severity of the Black Death. In China, the 13th century Mongol conquest disrupted farming and trading, and led to widespread famine. The population dropped from approximately 120 to 60 million. The 14th century plague is estimated to have killed 1/3 of the population of China.

In Europe, the Medieval Warm Period

Medieval Warm Period

The Medieval Warm Period , Medieval Climate Optimum, or Medieval Climatic Anomaly was a time of warm climate in the North Atlantic region, that may also have been related to other climate events around the world during that time, including in China, New Zealand, and other countries lasting from...

 ended sometime towards the end of the 13th century, bringing harsher winters and reduced harvests. In the years 1315 to 1317 a catastrophic famine, known as the Great Famine

Great Famine of 1315–1317

The Great Famine of 1315–1317 was the first of a series of large scale crises that struck Northern Europe early in the fourteenth century...

, struck much of North-West Europe

North-West Europe

North-West Europe is a term that refers to a northern area of Western Europe, although the exact area or countries it comprises varies.-Geographic definition:...

. The famine came about as the result of a large population growth in the previous centuries, with the result that, in the early 14th century the population began to exceed the number that could be sustained by productive capacity of the land and farmers.

In Northern Europe, new technological innovations such as the heavy plough and the three-field system

Crop rotation

Crop rotation is the practice of growing a series of dissimilar types of crops in the same area in sequential seasons.Crop rotation confers various benefits to the soil. A traditional element of crop rotation is the replenishment of nitrogen through the use of green manure in sequence with cereals...

 were not as effective in clearing new fields for harvest as they were in the Mediterranean because the north had poor, clay-like, soil. Food shortages and skyrocketing prices were a fact of life for as much as a century before the plague. Wheat, oats, hay, and consequently livestock, were all in short supply, and their scarcity resulted in hunger and malnutrition. The result was a mounting human vulnerability to disease, due to weakened immune systems.

The European economy entered a vicious circle

Virtuous circle and vicious circle

A virtuous circle and a vicious circle are economic terms. They refer to a complex of events that reinforces itself through a feedback loop. A virtuous circle has favorable results, while a vicious circle has detrimental results...

 in which hunger and chronic, low-level debilitating disease reduced the productivity

Productivity

Productivity is a measure of the efficiency of production. Productivity is a ratio of what is produced to what is required to produce it. Usually this ratio is in the form of an average, expressing the total output divided by the total input...

 of labourers, and so the grain output was reduced, causing grain prices to increase. This situation was worsened when landowners and monarchs like Edward III of England

Edward III of England

Edward III was King of England from 1327 until his death and is noted for his military success. Restoring royal authority after the disastrous reign of his father, Edward II, Edward III went on to transform the Kingdom of England into one of the most formidable military powers in Europe...

 (r. 1327–1377) and Philip VI of France

Philip VI of France

Philip VI , known as the Fortunate and of Valois, was the King of France from 1328 to his death. He was also Count of Anjou, Maine, and Valois from 1325 to 1328...

 (r. 1328–1350), out of a fear that their comparatively high standard of living would decline, raised the fines and rents of their tenants. Standards of living then fell drastically, diets grew more limited, and Europeans as a whole experienced more health problems.

In the autumn of 1314, heavy rains began to fall, which led to several years of cold and wet winters. The already weak harvests of the north suffered and the seven-year famine ensued. The Great Famine was the worst in European history, reducing the population by at least ten percent. Records recreated from dendrochronological

Dendrochronology

Dendrochronology or tree-ring dating is the scientific method of dating based on the analysis of patterns of tree-rings. Dendrochronology can date the time at which tree rings were formed, in many types of wood, to the exact calendar year...

 studies show a hiatus in building construction during the period, as well as a deterioration in climate.

This was the economic and social situation in which the predictor of the coming disaster, a typhoid

Typhoid fever

Typhoid fever, also known as Typhoid, is a common worldwide bacterial disease, transmitted by the ingestion of food or water contaminated with the feces of an infected person, which contain the bacterium Salmonella enterica, serovar Typhi...

 (Infected Water) epidemic, emerged. Many thousands died in populated urban centres, most significantly Ypres

Ypres

Ypres is a Belgian municipality located in the Flemish province of West Flanders. The municipality comprises the city of Ypres and the villages of Boezinge, Brielen, Dikkebus, Elverdinge, Hollebeke, Sint-Jan, Vlamertinge, Voormezele, Zillebeke, and Zuidschote...

. In 1318 a pestilence of unknown origin, sometimes identified as anthrax

Anthrax

Anthrax is an acute disease caused by the bacterium Bacillus anthracis. Most forms of the disease are lethal, and it affects both humans and other animals...

, targeted the animals of Europe, notably sheep and cattle, further reducing the food supply and income of the peasantry.

Middle Eastern outbreak

The plague struck various countries in the Middle East during the pandemic

Pandemic

A pandemic is an epidemic of infectious disease that is spreading through human populations across a large region; for instance multiple continents, or even worldwide. A widespread endemic disease that is stable in terms of how many people are getting sick from it is not a pandemic...

, leading to serious depopulation and permanent change in both economic and social structures. As it spread to western Europe, the disease also entered the region from southern Russia. By autumn 1347, the plague reached Alexandria

Alexandria

Alexandria is the second-largest city of Egypt, with a population of 4.1 million, extending about along the coast of the Mediterranean Sea in the north central part of the country; it is also the largest city lying directly on the Mediterranean coast. It is Egypt's largest seaport, serving...

 in Egypt

Egypt

Egypt , officially the Arab Republic of Egypt, Arabic: , is a country mainly in North Africa, with the Sinai Peninsula forming a land bridge in Southwest Asia. Egypt is thus a transcontinental country, and a major power in Africa, the Mediterranean Basin, the Middle East and the Muslim world...

, probably through the port's trade with Constantinople

Constantinople

Constantinople was the capital of the Roman, Eastern Roman, Byzantine, Latin, and Ottoman Empires. Throughout most of the Middle Ages, Constantinople was Europe's largest and wealthiest city.-Names:...

, and ports on the Black Sea

Black Sea

The Black Sea is bounded by Europe, Anatolia and the Caucasus and is ultimately connected to the Atlantic Ocean via the Mediterranean and the Aegean seas and various straits. The Bosphorus strait connects it to the Sea of Marmara, and the strait of the Dardanelles connects that sea to the Aegean...

. During 1348, the disease traveled eastward to Gaza

Gaza

Gaza , also referred to as Gaza City, is a Palestinian city in the Gaza Strip, with a population of about 450,000, making it the largest city in the Palestinian territories.Inhabited since at least the 15th century BC,...

, and north along the eastern coast to cities in Lebanon

Lebanon

Lebanon , officially the Republic of LebanonRepublic of Lebanon is the most common term used by Lebanese government agencies. The term Lebanese Republic, a literal translation of the official Arabic and French names that is not used in today's world. Arabic is the most common language spoken among...

, Syria

Syria

Syria , officially the Syrian Arab Republic , is a country in Western Asia, bordering Lebanon and the Mediterranean Sea to the West, Turkey to the north, Iraq to the east, Jordan to the south, and Israel to the southwest....

, and Palestine

Palestine

Palestine is a conventional name, among others, used to describe the geographic region between the Mediterranean Sea and the Jordan River, and various adjoining lands....

, including Ashkelon

Ashkelon

Ashkelon is a coastal city in the South District of Israel on the Mediterranean coast, south of Tel Aviv, and north of the border with the Gaza Strip. The ancient seaport of Ashkelon dates back to the Neolithic Age...

, Acre

Acre, Israel

Acre , is a city in the Western Galilee region of northern Israel at the northern extremity of Haifa Bay. Acre is one of the oldest continuously inhabited sites in the country....

, Jerusalem, Sidon

Sidon

Sidon or Saïda is the third-largest city in Lebanon. It is located in the South Governorate of Lebanon, on the Mediterranean coast, about 40 km north of Tyre and 40 km south of the capital Beirut. In Genesis, Sidon is the son of Canaan the grandson of Noah...

, Damascus

Damascus

Damascus , commonly known in Syria as Al Sham , and as the City of Jasmine , is the capital and the second largest city of Syria after Aleppo, both are part of the country's 14 governorates. In addition to being one of the oldest continuously inhabited cities in the world, Damascus is a major...

, Homs

Homs

Homs , previously known as Emesa , is a city in western Syria and the capital of the Homs Governorate. It is above sea level and is located north of Damascus...

, and Aleppo

Aleppo

Aleppo is the largest city in Syria and the capital of Aleppo Governorate, the most populous Syrian governorate. With an official population of 2,301,570 , expanding to over 2.5 million in the metropolitan area, it is also one of the largest cities in the Levant...

. In 1348–49, the disease reached Antioch

Antioch

Antioch on the Orontes was an ancient city on the eastern side of the Orontes River. It is near the modern city of Antakya, Turkey.Founded near the end of the 4th century BC by Seleucus I Nicator, one of Alexander the Great's generals, Antioch eventually rivaled Alexandria as the chief city of the...

. The city's residents fled to the north, most of them dying during the journey, but the infection had been spread to the people of Asia Minor

Anatolia

Anatolia is a geographic and historical term denoting the westernmost protrusion of Asia, comprising the majority of the Republic of Turkey...

.

Mecca

Mecca

Mecca is a city in the Hijaz and the capital of Makkah province in Saudi Arabia. The city is located inland from Jeddah in a narrow valley at a height of above sea level...

 became infected in 1349. During the same year, records show the city of Mawsil (Mosul

Mosul

Mosul , is a city in northern Iraq and the capital of the Ninawa Governorate, some northwest of Baghdad. The original city stands on the west bank of the Tigris River, opposite the ancient Assyrian city of Nineveh on the east bank, but the metropolitan area has now grown to encompass substantial...

) suffered a massive epidemic, and the city of Baghdad

Baghdad

Baghdad is the capital of Iraq, as well as the coterminous Baghdad Governorate. The population of Baghdad in 2011 is approximately 7,216,040...

 experienced a second round of the disease. In 1351, Yemen experienced an outbreak of the plague. This coincided with the return of King Mujahid of Yemen

Yemen

The Republic of Yemen , commonly known as Yemen , is a country located in the Middle East, occupying the southwestern to southern end of the Arabian Peninsula. It is bordered by Saudi Arabia to the north, the Red Sea to the west, and Oman to the east....

 from imprisonment in Cairo

Cairo

Cairo , is the capital of Egypt and the largest city in the Arab world and Africa, and the 16th largest metropolitan area in the world. Nicknamed "The City of a Thousand Minarets" for its preponderance of Islamic architecture, Cairo has long been a centre of the region's political and cultural life...

. His party may have brought the disease with them from Egypt.

Recurrence

In England, in the absence of census figures, historians propose a range of pre-incident population figures from as high as 7 million to as low as 4 million in 1300, and a post-incident population figure as low as 2 million. By the end of 1350 the Black Death had subsided, but it never really died out in England over the next few hundred years: there were further outbreaks in 1361–62, 1369, 1379–83, 1389–93, and throughout the first half of the 15th century. The plague often killed 10% of a community in less than a year — in the worst epidemics, such as at Norwich

Norwich

Norwich is a city in England. It is the regional administrative centre and county town of Norfolk. During the 11th century, Norwich was the largest city in England after London, and one of the most important places in the kingdom...

 in 1579 and Newcastle

Newcastle upon Tyne

Newcastle upon Tyne is a city and metropolitan borough of Tyne and Wear, in North East England. Historically a part of Northumberland, it is situated on the north bank of the River Tyne...

 in 1636, as many as 30 or 40%. The most general outbreaks in Tudor and Stuart England, all coinciding with years of plague in Germany and the Low Countries

Low Countries

The Low Countries are the historical lands around the low-lying delta of the Rhine, Scheldt, and Meuse rivers, including the modern countries of Belgium, the Netherlands, Luxembourg and parts of northern France and western Germany....

, seem to have begun in 1498, 1535, 1543, 1563, 1589, 1603, 1625, and 1636.

The plague repeatedly returned to haunt Europe and the Mediterranean throughout the fourteenth to 17th centuries, and although bubonic plague still occurs in isolated cases today, the Great Plague of London

Great Plague of London

The Great Plague was a massive outbreak of disease in the Kingdom of England that killed an estimated 100,000 people, 20% of London's population. The disease is identified as bubonic plague, an infection by the bacterium Yersinia pestis, transmitted through a flea vector...

 in 1665–1666 is generally recognized as one of the last major outbreaks.

The plague of 1575–77 claimed some 50,000 victims in Venice

Venice

Venice is a city in northern Italy which is renowned for the beauty of its setting, its architecture and its artworks. It is the capital of the Veneto region...

. In 1634, an outbreak of plague killed 15,000 Munich

Munich

Munich The city's motto is "" . Before 2006, it was "Weltstadt mit Herz" . Its native name, , is derived from the Old High German Munichen, meaning "by the monks' place". The city's name derives from the monks of the Benedictine order who founded the city; hence the monk depicted on the city's coat...

 residents. Late outbreaks in central Europe include the Italian Plague of 1629–1631, which is associated with troop movements during the Thirty Years' War

Thirty Years' War

The Thirty Years' War was fought primarily in what is now Germany, and at various points involved most countries in Europe. It was one of the most destructive conflicts in European history....

, and the Great Plague of Vienna

Great Plague of Vienna

The Great Plague of Vienna occurred in 1679 in Vienna, Austria, the imperial residence of the Austrian Habsburg rulers. From contemporary descriptions, the disease is believed to have been bubonic plague, which is caused by the bacterium Yersinia pestis, carried by fleas associated with the black...

 in 1679. About 200,000 people in Moscow

Moscow

Moscow is the capital, the most populous city, and the most populous federal subject of Russia. The city is a major political, economic, cultural, scientific, religious, financial, educational, and transportation centre of Russia and the continent...

 died of the disease from 1654 to 1656. The last plague outbreak ravaged Oslo

Oslo

Oslo is a municipality, as well as the capital and most populous city in Norway. As a municipality , it was established on 1 January 1838. Founded around 1048 by King Harald III of Norway, the city was largely destroyed by fire in 1624. The city was moved under the reign of Denmark–Norway's King...

 in 1654. In 1656 the plague killed about half of Naples

Naples

Naples is a city in Southern Italy, situated on the country's west coast by the Gulf of Naples. Lying between two notable volcanic regions, Mount Vesuvius and the Phlegraean Fields, it is the capital of the region of Campania and of the province of Naples...

' 300,000 inhabitants. Amsterdam

Amsterdam

Amsterdam is the largest city and the capital of the Netherlands. The current position of Amsterdam as capital city of the Kingdom of the Netherlands is governed by the constitution of August 24, 1815 and its successors. Amsterdam has a population of 783,364 within city limits, an urban population...

 was ravaged in 1663–1664, with a mortality given as 50,000.

A plague epidemic that followed the Great Northern War

Great Northern War

The Great Northern War was a conflict in which a coalition led by the Tsardom of Russia successfully contested the supremacy of the Swedish Empire in northern Central Europe and Eastern Europe. The initial leaders of the anti-Swedish alliance were Peter I the Great of Russia, Frederick IV of...

 (1700–1721, Sweden

Sweden

Sweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe. Sweden borders with Norway and Finland and is connected to Denmark by a bridge-tunnel across the Öresund....

 v. Russia and allies) wiped out almost 1/3 of the population in the region. An estimated one-third of East Prussia

East Prussia

East Prussia is the main part of the region of Prussia along the southeastern Baltic Coast from the 13th century to the end of World War II in May 1945. From 1772–1829 and 1878–1945, the Province of East Prussia was part of the German state of Prussia. The capital city was Königsberg.East Prussia...

's population died in the plague of 1709–1711. The plague of 1710 killed two-thirds of the inhabitants of Helsinki

Helsinki

Helsinki is the capital and largest city in Finland. It is in the region of Uusimaa, located in southern Finland, on the shore of the Gulf of Finland, an arm of the Baltic Sea. The population of the city of Helsinki is , making it by far the most populous municipality in Finland. Helsinki is...

. An outbreak of plague between 1710 and 1711 claimed a third of Stockholm

Stockholm

Stockholm is the capital and the largest city of Sweden and constitutes the most populated urban area in Scandinavia. Stockholm is the most populous city in Sweden, with a population of 851,155 in the municipality , 1.37 million in the urban area , and around 2.1 million in the metropolitan area...

’s population.

During the Great Plague of 1738

Great Plague of 1738

The Great Plague of 1738 was an outbreak of the bubonic plague between 1738-1740 that affected areas in the modern nations of Romania, Hungary, Ukraine, Serbia, Croatia, and Austria...

, the epidemic struck again, this time in Eastern Europe, spreading from Ukraine

Ukraine

Ukraine is a country in Eastern Europe. It has an area of 603,628 km², making it the second largest contiguous country on the European continent, after Russia...

 to the Adriatic Sea

Adriatic Sea

The Adriatic Sea is a body of water separating the Italian Peninsula from the Balkan peninsula, and the system of the Apennine Mountains from that of the Dinaric Alps and adjacent ranges...

, then onwards by ship to infect some in Tunisia

Tunisia

Tunisia , officially the Tunisian RepublicThe long name of Tunisia in other languages used in the country is: , is the northernmost country in Africa. It is a Maghreb country and is bordered by Algeria to the west, Libya to the southeast, and the Mediterranean Sea to the north and east. Its area...

. The destruction in several cities in what is now Romania

Romania

Romania is a country located at the crossroads of Central and Southeastern Europe, on the Lower Danube, within and outside the Carpathian arch, bordering on the Black Sea...

 (such as Timişoara

Timisoara

Timișoara is the capital city of Timiș County, in western Romania. One of the largest Romanian cities, with an estimated population of 311,586 inhabitants , and considered the informal capital city of the historical region of Banat, Timișoara is the main social, economic and cultural center in the...

) was formidable, claiming tens of thousands of lives.