After initial defensive successes in the east, the year 1944 saw the collapse of Army Group Center in the summer of 1944. In the autumn of 1944, the Soviet army advanced into German territory for the first time and exacted brutal revenge on the civilian population. Romania, Bulgaria, and Finland defected from the alliance and switched sides. Hungary was occupied. The Balkans had to be gradually evacuated. In Italy, weak German forces managed to temporarily halt the Allied advance at Monte Cassino. Rome fell only in June 1944. With the invasion of Normandy on June 6, 1944, the Allies returned to the Western European theater of war. Their advance through France and Belgium led to the fall of the first German city in the west: Aachen. One German city after another fell victim to the bombs of the Allies. The deployment of the wonder weapons "V1" and "V2" followed.