caption The 1988 Halabja attack became known as the worst chemical weapons attack in modern history

Some Kurdish fighters had previously fought alongside Saddam Hussein's forces in the war against Iran, but many Peshmerga then allied with Iranian troops in order to bring more areas in Iraqi Kurdistan under their control.

Saddam Hussein then began a campaign of collective punishment known as the "Anfal" against the Kurds, for fighting with Iranian forces and for seeking more territory.

The most notorious event in the Anfal campaign was the 1988 Halabja chemical weapons attack , in southern Kurdistan. An estimated 5,000 people, mostly women and children, were killed when Iraqi jets dropped poison gas on the town. Thousands of inhabitants choked on a mixture of mustard gas and nerve agents.

As a result, thePeshmerga were forced to cease operations as more than a million Kurds were displaced, and hundreds of thousands killed throughout the Anfal campaign.

Conflict with Saddam

image copyright AP image caption Elite units of female Peshmerga fighters have been trained by SWAT teams to fight IS militants in Iraq

Throughout the 1990s and in the aftermath of the Anfal campaign, despite huge losses the Peshmerga continued to battle Iraqi forces against the backdrop of the First Gulf War and Operation Desert Storm.

However, internal tensions continued to build and turned to war between the two rival Kurdish factions, the Kurdistan Democratic Party (KDP) led by Massoud Barzani, son of the Kurdish nationalist leader Mustafa Barzani and the Patriotic Union of Kurdistan (PUK) led by Jalal Talabani, who would eventually become Iraqi president.

During