Heeresgruppe E
After the September advance through Romania and Bulgaria in October 1944, The Red Army, together with Yugoslav forces, took Belgrade (central communication node of the Balkans) in the Belgrade Offensive. Due to Yugoslav partisan activity, the Yugoslav-Allied Operation Ratweek, and pressure from the Bulgarian Army, the Germans failed to prevent this while they awaited the redeployment of Army Group E troops from Greece. The Red Army decided to exploit this delay and continued to advance with the 3rd Ukrainian Front from Belgrade to south-west Hungary. The aim of the advance was to separate and protect their main attack in Hungary from attacks on the flank by Army Group E from the south.