Heeresgruppe F
After the Second Jassy–Kishinev Offensive, a wide and deep area of possible advancement opened up in front of the Red Army. This started a race between the Soviets and the Germans to the "Blue Line", an intended front-line running from the southern slopes of the Carpathians over the Iron Gates down the Yugoslav-Bulgarian border. By the end of September, both the 2nd and the 3rd Ukrainian Front managed to deploy some 19 Rifle Divisions with supporting units to the line (compared to 91 Rifle Divisions in the Second Jassy–Kishinev Offensive). Vast terrain with poor and damaged roads, uncertainty over local forces, and logistical difficulties dispersed the German groups and slowed down their advancement. On the other side, Army Group F encountered much larger problems in concentrating their forces. This resulted in the Red Army achieving substantial superiority in numbers on the Blue Line by the end of September. Given this fact, and the prospect of cooperation with NOVJ, the offensive was launched.