Soviet troops first entered Romanian territory in March 1944, during the Uman-Botoșani offensive, capturing several towns in northern Moldavia including Botoșani. Encouraged by these gains, the Soviet high command launched the first Jassy-Kishinev offensive between April 8 and June 6, aiming to cut Axis defensive lines in northern Romania and open the door to the Balkans. The operation was named after the two major cities in the operational area: Iași, known to the Russians as Jassy, and Chișinău, known as Kishinev. It failed. Military historian David Glantz attributed the defeat to poor Soviet combat performance and effective German defensive preparations. The Romanian and German forces held their positions through the spring and into summer, and for a few months it appeared the Eastern Front might stabilize in the region. It did not.

The second Jassy-Kishinev offensive, launched on August 20, 1944, was a fundamentally different operation from the spring attempt. The Soviets had reinforced, reorganized, and learned from their earlier mistakes. The attack struck with overwhelming force, and within days the German Sixth Army was encircled. Romanian units, already demoralized and questioning their alliance with Germany, began surrendering or retreating. On August 23, in the middle of the offensive, King Michael of Romania staged a coup d'état against Prime Minister Ion Antonescu, who had allied Romania with Nazi Germany. The new government immediately surrendered to the Allies and declared war on Germany. Romanian soldiers who had been fighting alongside the Wehrmacht were now ordered to fight against it. The Axis front did not merely retreat -- it disintegrated.

The consequences cascaded across southeastern Europe. In the north, the German Eighth Army retreated toward Hungary, suffering heavy losses. Across the rest of Romania, German units found themselves cut off and surrounded. A large security and anti-aircraft force guarding the strategically vital Ploiești oil fields -- which had fueled much of the German war machine -- was captured. Fragments of German forces fought their way through the Carpathian mountain passes toward Hungary, battling both Soviet troops and the Romanian forces that had just switched sides. Romanian soldiers held several key mountain passes, accelerating the German retreat. On August 26, Bulgaria withdrew from the Axis, and Soviet forces invaded it on September 8. By September 24, nearly all of Romania was under Soviet control. The speed of the collapse stunned both sides.

Romania's switch to the Allied side did not bring the liberation its new government had hoped for. The Soviet forces, now moving through Romanian territory without military opposition, captured approximately 120,000 Romanian soldiers and transported them to labor camps deep inside the Soviet Union. Many of these men -- soldiers who had been fighting on the Soviet side for barely a month -- perished from forced labor, malnutrition, and the brutal conditions of Soviet captivity. Romania itself fell firmly into the Soviet sphere of influence, beginning four decades of communist rule. Meanwhile, the German and Hungarian forces regrouped in Hungary, where Hitler declared Budapest a fortress city to be defended at all costs. The Battle of Budapest that followed, lasting from late 1944 into February 1945, became one of the war's bloodiest urban sieges. What had begun as a campaign in Romanian fields and river valleys ended in door-to-door fighting through the streets of a capital city 500 kilometers to the northwest.