After the First World War, the Pirin part of Macedonia was belonging to Bulgaria with 6.798 sq. Km. and about 250.000 habitants. 96% of them were Macedonians. Huge number of them emigrated in Bulgaria. Their tragic status was misused for the achievement of the Great Bulgarian interests to rule over Macedonia.

Prominent Macedonian revolutionaries performed activities among the Macedonian emigration in Bulgaria. The former VMRO leaders of Seres persevered in advocating the Macedonian interests. They, organized into a Provisional Agency of the former VMRO (Gj.Petrov, D.Hadji Dimov, P.Pop Arsov etc.), performed activities in order to win the World publicity declaring at the Paris Peace Conference for the establishment of an independent Macedonian state. The activity of the agency annoyed the government circles in Bulgaria which activated the vrhovized Executive Committee of the Macedonian brotherhoods; it declared before the international forums against the interests of the Macedonian people. The Macedonian brotherhoods in Bulgaria were polarized. Some of them performed a significant national and cultural activity, such as: the Kukush (Kilkis) and Gevgelia brotherhoods.

After the War, the so called "autonomic" VMRO was active, led by T.Alexandrov, who although declared for the autonomy of Macedonia advocated the idea of vrhovism and of the loyal court. Turning into a terrorist organization, the VMRO caused damage to the Macedonian national liberation movement executing a great number of political assassinations of prominent Macedonians (Yané Sandanski, Gjorche Petrov, Dimo Hadji Dimov, Todor Panitsa etc.). The European publicity was disgusted with its terrorist activity. In the Pirin part of Macedonia the vrhovist VMRO outgrew into the special "state within a state". The organization executed terrorist actions in the Vardar part of Macedonia. After the assassination of Todor Alexandrov and the election of Vancho Mihailov at the head of VMRO, numerous terrorist actions were executed and a great number of Macedonians - patriots and communists were killed.

The legal Ilinden organization used to be very active in the Macedonian emigration, publishing the magazines: "Ilinden", "Pirin" and others.

The VMRO (United) was founded in Vienna in 1925 under the auspices of the Balkan Communist Federation and the Comintern, also performed activity in the Pirin part of Macedonia.

During the period between the two World Wars the Macedonians in Bulgaria performed intensive national and cultural activity. Numerous newspapers were published on Macedonian: "Ilinden", "Makedonsko zname" ("Macedonian Flag"), "Makedonski vesti" ("Macedonian News"), "Obedinist" ("The Uniter").