In 1919 he was one of the founders, and in 1920—1928 was the chairman of the
Military Union, an officers' organization. As its head, Valkov took part in the
Bulgarian coup d'état of 9 June 1923, in which they overthrew
Prime Minister Aleksandar Stamboliyski. From 10 June 1923 until 11 January 1929, Valkov was the Minister of War in the governments of prime ministers
Aleksandar Tsankov and
Andrey Lyapchev. He oversaw the repression of
leftist organizations after the September Rebellion in 1923 and the assassination attempt on Tsar
Boris III of Bulgaria two years later. Valkov was also one of the founders of a military factor in Kazanlak. In October 1925, at the time of the
Greco-Bulgarian conflict in the Petrich district, General Valkov used diplomatic rather than military means to restore the status-quo. He gave the order to not open fire and appealed to the
League of Nations for support. As a result,
Greece was recognized as the aggressor and was forced to pay Bulgaria compensation for casualties and damage. The results of the conflict are regarded as a success of Bulgarian diplomacy. In the second half of the 1920s, Valkov was accused of backing
Ivan Mihailov and his faction of the internal conflict within the
Internal Macedonian Revolutionary Organization. His actions were criticized by former Prime Minister Aleksandar Tsankov and the
Minister of Foreign Affairs,
Atanas Burov, but Valkov received support from Boris III at the time. It was because of this that the general remained in the government. In 1928 Valkov declared the dissolution of the Military Union due to it being divided as a result of internal bickering and political differences. At a time when negotiations were underway regarding Bulgaria's representation in international organizations, the government demanded the Valkov resign because of his reputation of being an opponent of democracy. Prime Minister Lyapchev agreed to this, and Valkov was removed from his post as war minister. == Later career ==