South Sudan won independence from Sudan in 2011 after decades of civil war. Violence erupted in late 2013 after Kiir, from the Dinka ethnic group, sacked vice-president Riek Machar, a Nuer.
The two men have signed many deals to end a war estimated to have killed more than 400,000 people. They repeatedly pushed back deadlines to form a government of national unity, but in 2020 finally did so.
Despite the peace deal, violence is still raging in parts of the country, according to UN reports.