In September 1998, Barzani and Talabani signed the U.S.-mediated Washington Agreement establishing a formal peace treaty. In the agreement, the parties agreed to share revenue, share power, deny the use of northern Iraq to the PKK, and not allow Iraqi troops into the Kurdish regions. The United States pledged to use military force to protect the Kurds from possible aggression by Saddam Hussein. At the same time, implementation of the U.N. Oil-for-Food Programme brought revenue to northern Iraq, allowing for increased standards of living. Iraqi Kurdistan became a relatively peaceful region, before the terrorist group Ansar al-Islam entered the area in December 2001, bringing renewed conflict. Around a month later, U.S. President Bill Clinton signed the Iraq Liberation Act into law, providing for military assistance to Iraqi opposition groups, including the PUK and KDP. The KDP estimated that 58,000 of its supporters had been expelled from PUK-controlled regions from October 1996 to October 1997. The PUK says 49,000 of its supporters were expelled from KDP-controlled regions from August 1996 to December 1997. The PUK and KDP later co-operated with American forces during the 2003 invasion of Iraq, routing Iraqi forces with the help of American air power and overrunning much of northern Iraq including the cities of Kirkuk and Mosul. After the invasion, Massoud Barzani was later elected president of Iraqi Kurdistan while Jalal Talabani was elected President of Iraq.
Question: What happened first: the U.S.-mediated Washington Agreement or PUK and KDP later co-operated?
Answer: Washington Agreement; the U.S.-mediated Washington Agreement; U.S.-mediated Washington Agreement; U.S.-mediated Washington Agreement