After the First World War the combined Macedonian-Thracian revolutionary movement separated into two detached organizations, IMRO and ITRO. After this moment the IMRO earned a reputation as an ultimate terror network, seeking to change state frontiers in the Macedonian regions of Greece and Serbia (later Yugoslavia). They contested the partitioning of Macedonia and launched raids from their Petrich stronghold into Greek and Yugoslav territory. Their base of operation in Bulgaria was jeopardized by the Treaty of Niš, and the IMRO reacted by assassinating Bulgarian prime minister Aleksandar Stamboliyski in 1923, with the cooperation of other Bulgarian elements opposed to him. In 1925 the Greek army launched a cross-border operation to reduce the IMRO base area, but it was ultimately stopped by the League of Nations, and IMRO attacks resumed. In the interwar period the IMRO also cooperated with the Croatian Ustaše, and their ultimate victim was Alexander I of Yugoslavia, assassinated in France in 1934. After the Bulgarian coup d'état of 1934, their Petrich stronghold was subjected to military crackdown by the Bulgarian army, and the IMRO was reduced to a marginal phenomenon.