The Soviet Union invaded Hungary, one of Hitler's allies in September 1944, as it drove Nazi forces back towards Germany.
Soviet troops occupied Hungary and continued to do so until the end of the war, even though an Allied Control Commission for Hungary was set up to run the country.
The ACC comprised (consisted of) the Soviet Union, the USA and the UK, however the Soviet union was the most influential of all the powers and was able to determine events in Hungary in the immediate post-war years.