The Polish–Ukrainian War, from November 1918 to July 1919, was a conflict between the Second Polish Republic and Ukrainian forces (both the West Ukrainian People's Republic and Ukrainian People's Republic). The conflict had its roots in ethnic, cultural and political differences between the Polish and Ukrainian populations living in the region, as Poland and both Ukrainian republics were successor states to the dissolved Russian and Austrian empires. The war started in Eastern Galicia after the dissolution of the Austro-Hungarian Empire and spilled over into Chełm Land and Volhynia (Wołyń) regions formerly belonging to the Russian Empire, which were both claimed by the Ukrainian State (a client state of the German Empire) and the Ukrainian People's Republic. Poland re-occupied the disputed territory on 18 July 1919.