The Polish-Soviet War (February 1919 - March 1921) was an armed conflict that pitted Soviet Russia and Soviet Ukraine against the Second Polish Republic and the Ukrainian People's Republic over the control of an area equivalent to today's Ukraine and parts of modern-day Belarus. At some points the war also threatened Poland's existence as an independent state. It followed on from the Soviet westward offensive of 1918-19. A formal peace treaty, the Peace of Riga, was signed on 18 March 1921, dividing the disputed territories between Poland and Soviet Russia. The war largely determined the Soviet-Polish border for the period between the World Wars. Much of the territory ceded to Poland in the Treaty of Riga became part of the Soviet Union after World War II, when Poland's eastern borders were redefined by the Allies in close accordance with the British-drawn Curzon Line of 1920.