During the Polish–Soviet War of 1919-1921, Soviet Russia and Soviet Ukraine were in combat with the re-established Second Polish Republic and the newly established Ukrainian People's Republic. Both sides aimed to secure territory in the often disputed areas of the Kresy, which make up today's Ukraine and parts of modern-day Belarus, in the context of the fluidity of borders in Central and Eastern Europe in the aftermath of World War I and the breakdown of the Austrian, German, and Russian empires. The first clashes between the two sides occurred in February 1919, but full-scale war did not break out until the following year. Especially at first, neither Soviet Russia, embroiled in the Russian Civil War, nor Poland, still in the early stages of state re-building, were in a position to formulate and pursue clear and consistent war aims.