The First Islamic Civil War (656–661), also called the First Fitna ( "The Fitna of the killing of Uthman"), was the first major civil war

Civil war

A civil war is a war between organized groups within the same nation state or republic, or, less commonly, between two countries created from a formerly-united nation state....

 within the Islamic Caliphate. It arose as a struggle over who had the legitimate right to become the ruling Caliph

Caliph

The Caliph is the head of state in a Caliphate, and the title for the ruler of the Islamic Ummah, an Islamic community ruled by the Shari'ah. It is a transcribed version of the Arabic word   which means "successor" or "representative"...

. The dispute shattered the unity of the Muslim ummah

Ummah

Ummah is an Arabic word meaning "community" or "nation." It is commonly used to mean either the collective nation of states, or the whole Arab world...

 and set into motion long-term trends that ended in the division of Islam into Shi'a and Sunni

Sunni Islam

Sunni Islam is the largest branch of Islam. Sunni Muslims are referred to in Arabic as ʾAhl ūs-Sunnah wa āl-Ǧamāʿah or ʾAhl ūs-Sunnah for short; in English, they are known as Sunni Muslims, Sunnis or Sunnites....

 sects.

The Fitna began as a series of revolts fought against first Imam Ali ibn Abi Talib, and the fourth and final of the Sunni Rightly Guided Caliphs

Rashidun

The Rightly Guided Caliphs or The Righteous Caliphs is a term used in Sunni Islam to refer to the first four Caliphs who established the Rashidun Caliphate. The concept of "Rightly Guided Caliphs" originated with the Abbasid Dynasty...

, caused by the controversial assassination of his predecessor, Uthman Ibn Affan.