The Internal Macedonian Revolutionary Organization (IMRO; Bulgarian: Вътрешна македонска революционна организация (ВМРО), romanized: Vatreshna Makedonska Revolyutsionna Organizatsiya (VMRO); Macedonian: Внатрешна македонска револуционерна организација (ВМРО), romanized: Vnatrešna Makedonska Revolucionerna Organizacija (VMRO)), was a secret revolutionary society founded in the Ottoman territories in Europe, that operated in the late 19th and early 20th centuries.
Founded in 1893 in Salonica, it sought sovereignty for Macedonia under the slogan Macedonia for the Macedonians. Initially it aimed to gain autonomy for Macedonia and Adrianople regions in the Ottoman Empire, however, it later became an agent serving Bulgarian interests in Balkan politics. IMRO modeled itself after the earlier Bulgarian Internal Revolutionary Organization of Vasil Levski and accepted its motto "Freedom or Death" (Свобода или смърть). According to the memoirs of some founding and ordinary members, in the Organization's earliest statute from 1894, the membership was reserved exclusively for Bulgarians. This was later changed on the initiative of Gotse Delchev, who wanted IMRO to depart from its exclusively Bulgarian nature, so he opened the membership for all inhabitants of European Turkey and the organization begun to acquire a more separatist stance. However, these new formulas as a whole failed to attract other ethnic groups, from whom it was seen as a pro-Bulgarian society, thus IMRO remained with base only among Bulgarian Exarchist affiliated Slavic speakers in Ottoman Macedonia. It used the Bulgarian language in all its documents and in its correspondence. The Organisation founded in 1896 its Foreign Representation in Sofia, the capital of Bulgaria. Starting in the same year, it fought the Ottomans using guerrilla tactics, and in this, they were successful, even establishing a state within a state in some regions, including their tax collectors. This struggle escalated in 1903 with the Ilinden–Preobrazhenie Uprising. The fighting involved about 15,000 IMRO irregulars and 40,000 Ottoman soldiers, lasting for over seven weeks. After the uprising failed, and the Ottomans destroyed some 100 villages, the IMRO resorted to more systematic forms of terrorism targeting civilians. More important, the Ilinden disaster splintered IMRO and signalled the beginning of a fratricidal conflict between the left-wing faction ("federalists") who continued to favor autonomy as step towards independent Macedonia and its inclusion into a future Balkan Federation, and the right-wing faction ("centralists") which favored unification with Bulgaria. In fact, the division was a culmination of a conflict which existed within IMRO since its formation. It was based partially on ideology, and partly in terms of personality and locality, and it would plague the Macedonian revolutionary movement over the next decades.
