World War I ended on November 11, 1918 when Germany signed the Compiègne Armistice. On November 13, Soviet Russia renounced the Treaty of Brest-Litovsk and began the Soviet westward offensive of 1918-1919. The Bolsheviks followed retreating German troops and attacked Lithuania and Poland from the east trying to prevent their independence. They attempted to spread the global proletarian revolution, establish Soviet republics in the region, and join the German and the Hungarian Revolutions. The Soviet offensive sparked a series of local wars, including the Polish-Soviet War and the Lithuanian-Soviet War. At first, the Soviets were successful, but came to a halt in February 1919. In March-April both Lithuanians and Poles began their offensives against the Soviets. The three armies met in the Vilnius Region. Polish-Lithuanian relations at the time were not immediately hostile, but grew worse as each side refused to compromise. On April 19, 1919, the Polish Army captured Vilnius. At first, both Poles and Lithuanians cooperated against the Soviets, but soon the cooperation gave way to increasing hostility. Lithuania claimed neutrality in the Polish-Soviet War. As the Polish Army forced its way further into Lithuania, the first clashes between Polish and Lithuanian soldiers occurred on April 26 and May 8, 1919, near Vievis. Though there was no formal state of war and few casualties, by July newspapers reported increasing clashes between Poles and Lithuanians, primarily around the towns of Merkinė and Širvintos. Direct negotiations in Kaunas between May 28 and June 11, 1919, collapsed as neither side agreed to compromise. Lithuania tried to avoid direct military conflict and submitted its case for mediation to the Conference of Ambassadors.

What were the Polish-Soviet War and the Lithuanian-Soviet War caused by?
Soviet offensive