Two generations of Bulgarian freedom fighters. The one on the right was a veteran of the liberation war of 1876-1878.

While the Red Army was marching through the north-east Bulgaria to the cheers of the local population, 300km away, in Bulgaria's capital, more important events took place. The government of Konstantin Muravyev, trying to save its control over the country, severed diplomatic relations with Germany and asked the Soviet Union for cease-fire. Yet, those decisions were already hopelessly late. The Political Bureau of the Central Committee of the Bulgarian Workers' Party (communists) and the General Revolutionary Staff of the People's Revolutionary Army of Liberation (NOVA) deemed that moment best for the final armed uprising. It took place on 9 September 1944 at 2:00 in Sofia. To the operations in Sofia were detached Brigade Chavdar (commander Dobri Dzhurov, commissar Stefan Halachev), Shopski Detachment, and trusted units of the garrison of Sofia. In result of intensive partisan propaganda, with the uprising sided the 1st Battalion of the 1st Infantry Regiment, a tank regiment, a company of military cadets, an assault sapper battalion from the 1st Engineers Regiment, and a reflector group of the anti-aircraft battery of the Supreme Command. A special task was assigned to the 1st Sofian National-Liberation Division, armed with Soviet arms from parachuted supplies. It received orders do advance to Sofia, and with part of its forces to Pernik, to support local miners in the attack on a concentration camp for political prisoners, and seizure of power in the city.

The Political Bureau of the Central Committee of the Bulgarian Workers' Party (communists) and the General Revolutionary Staff of the People's Revolutionary Army of Liberation exercised the overall control over the uprising.

First of all, insurgents attacked the buildings of the Ministry of War, where the government resided. Within an hour the guards were disarmed; then started arrests of the ministers of the government, major state officials, and fascist officers. Next were seized buildings of the Ministry of Interior and other ministries, central post office and telegraph, and the central railway station. The attackers met no resistance; there were only isolated incidents involving fascist officers. Police surrendered without much problem as well. Whereas the 1st Infantry Division, that the government deployed for security in Sofia in the beginning of September, remained idle.

The uprising won. The Fatherland Front took power. Its government comprised representatives of the Bulgarian Workers' Party (communists), Bulgarian National Agrarian Union Pladne, coalition Zveno, Bulgarian Social Democratic Party, a group of independent democratic politicians and a group of democratic officers from the Military League. The leader of Zveno, Kimon Georgiev, became the prime-minister of the new government. His government severed all relations with Berlin, declared war on Germany, and established contacts with the Soviet government; in the radio-broadcast to the Bulgarian people Kimon Georgiev announced a programme of broad democratic reforms.

News about the uprising in Sofia quickly spread throughout the whole Bulgaria. It was a strong impulse to activate insurgent activities in the country. Partisans, soldiers and civilians started disarming the Germans, and replacing local authorities with new people. By the end of 9 September all powers in Bulgaria were in the hands of the Fatherland Front.

Once the uprising won and the new, democratic government declared war on Germany, further military operations in Bulgaria became unnecessary. Therefore, the Soviet Supreme Headquarters ordered the 3rd Ukrainian Front and the Black Sea Fleet to cease all operations on 9 September at 22:00. The order also pointed out that as a result of the successful actions of our troops the purpose of our operations has been attained: has broken off with Germany and declared war on her. In this way Bulgaria has ceased to be a bulwark of German imperialism in the Balkans as she had been in the course of the past thirty years. [Великая Отечественная война Советского Союза, 1941-1945: Краткая история. (1984).]

Striking Bulgaria out of the "Axis" of the fascist alliance, and her changing sides and joining the Allies was a big blow to the III Reich. The situation of the German forces in the Balkans had worsened dramatically. German communications between Greece and Yugoslavia, already under intensive partisan pressure, now became exposed to a direct attack of the Soviet forces. When the Soviet troops were within 360 to 400 km from the Bulgaro-Yugoslav border, the Germans started disarming Bulgarian units on occupation duty in Yugoslavia. Sofia, located close to the Yugoslav border, might be vulnerable to a possible German attack. To counter that threat it was decided to concentrate around the Bulgarian capital an autonomous grouping comprising the 34th Infantry Corps, 5th Motorized Brigade of Guards, 4th Mechanized Corps of Guards, 96th Armoured Brigade, 9th Anti-Tank Artillery Brigade, and auxiliary units. To provide the air cover, on 16 September on the airfields around Sofia were deployed the 288th Fighter Division, 306th Ground-Attack Division, and 244th Bomber Division.

Immediately after the victory of the uprising there began formation of the new Bulgarian army. This process had to be finalized quickly, as it was required to engage the Bulgarian forces against the Germans as soon as possible. Since most of the old army personnel joined the partisans and the new government, they were left in active service. Existing units were reinforced by partisans. In total as many as 38 thousand partisans with combat experience joined the army ranks. Also, 800 partisan commanders were assigned to officers' posts, and a number of reserve officers, veterans of the civil war in Spain (1936-1939), and veterans of the September Uprising of 1923 were recruited as political commissars.

On 17 September 1944 there was reached the agreement to transfer those Bulgarian units, which were ready for action, under the command of the 3rd Ukrainian Front. On 20 September, by orders from the Supreme Headquarters, Fyodor Tolbukhin (promoted to the rank of Marshal on 12 September) set his troops in motion. To the area Brisartsi - Montana - Vratsa - Mezdra was shifted the 57th Army with the orders to be prepared for moving westwards. In the area of Kazanlyk - Stara Zagora - Yambol - Burgas was deployed the 37th Army readied to cover the southern flank. In the west, from Chuprene on the Bulgaro-Yugoslav border to the border with Greece, were deployed Bulgarian 1st, 2nd and 4th Armies; the 3rd Army remained in reserve.

Such a deployment of the forces was optimal for further operations in Yugoslavia, and covered Bulgaria from the south. Also, strong anti-air defence was organized around Sofia.