State of Slovenes, Croats and Serbs
In 1918, the Austro-Hungarian Monarchy collapsed and the Syrmia region first became a part of the newly formed State of Slovenes, Croats and Serbs, and then, on 24 November 1918, the assembly of Syrmia in Ruma decided most of Syrmia (including Mitrovica) would join the Kingdom of Serbia.