The Budapest Offensive was Soviet Russia’s campaign to disable Hungary, the last Nazi ally, in 1944–45. Following the occupation of Romania in summer 1944, Soviet forces swept westwards into Hungary and southern Bulgaria. Budapest was isolated in December, and after a devastating siege the city fell on 13 February 1945. After the anti-Nazi Slovak uprising in August 1944, the Germans occupied Slovakia, which hitherto had been ‘independent’ with a large ethnically German minority. Guerrilla warfare by the insurgents pinned down German forces in Slovakia, which might otherwise have been involved in operations on the eastern front. By December 1944 Soviet and Romanian forces were beginning to occupy southern Slovakia, moving into the east in January and finally reaching northwestern Slovakia in March. Soviet forces marched into Bratislava on 4 April 1945.