Following earlier clashes between Polish and Russian troops, the Polish–Soviet War broke out in early 1920, with the Poles invading Ukraine and taking Kyiv on 7 May. On 26 May, Stalin was moved to Ukraine, on the Southwest Front. The Red Army retook Kyiv on 10 June and soon forced the Polish troops back into Poland. On 16 July, the Central Committee decided to take the war into Polish territory. Lenin believed that the Polish proletariat would rise up to support the Russians against Józef Piłsudski's Polish government. Stalin had cautioned against this; he believed that nationalism would lead the Polish working-classes to support their government's war effort. He also believed that the Red Army was ill-prepared to conduct an offensive war and that it would give White Armies a chance to resurface in Crimea, potentially reigniting the civil war. Stalin lost the argument, after which he accepted Lenin's decision and supported it. Along the Southwest Front, he became determined to conquer Lviv; in focusing on this goal he disobeyed orders in early August to transfer his troops to assist Mikhail Tukhachevsky's forces that were attacking Warsaw.