War I, he was captured by Austro-Hungarian forces and interned at the Boldagason internment camp in Hungary, where he grew strongly opposed to King Nikola. He was released after the war and moved to Zemun and worked as a lawyer there. He became a leading member of the "Greens" (zelenaši), a Montenegrin separatist movement which sided with the Yugoslav Federalist Party. During this time, he cooperated frequently with Croatian politicians such as Stjepan Radić, Vlatko Maček, and Ante Pavelić, with whom he became good friends. In the mid-1920s, Drljević founded the Montenegrin Federalist Party. He quickly became the party's sole leader and foremost theoretician. He expressed support for the unity of Yugoslavia and stressed Montenegro's loyalty to Serbian nationhood, but argued that a nation did not necessarily need to be part of a single state and hinted that he would support the restoration of Montenegro's independence. Consequently, the "Greens" demanded that Yugoslavia's internal boundaries be organized to match the borders of the Balkan states as they were prior to 1918. Drljević and Mihailo Ivanović had first attempted to found the Montenegrin Party for the 1920 election of a Constitutional Assembly, but were unable to do so due to a lack of time and resistance by the authorities. Drljević ran unsuccessfully for the Montenegrin Federalist Party in the 1923 elections in both the counties of Nikšić and Kolašin. He ran again in Kolašin in 1925 and was elected to the National Assembly. In 1927, Drljević was elected representative of the Zemun District on the electoral list of the Croatian Peasant Party (HSS). Afterwards, he helped solve a political rift between Radić and Serb politician Svetozar Pribićević, resulting in the formation of an HSS–Democratic Party coalition. The following year, Drljević unsuccessfully attempted to dissuade Radić from attending the National Assembly of the Kingdom of Serbs, Croats and Slovenes prior to his assassination by Serb politician Puniša Račić. World War II Montenegrin leader On 6 April 1941, Axis forces invaded Yugoslavia. Montenegro was invaded by the forces of Germany and Italy, with the Germans attacking from Bosnia and Herzegovina and the Italians from Albania. The Germans later withdrew, leaving the Italians to occupy the area. In the western portion of Yugoslavia, Pavelić, who had been in exile in Benito Mussolini's Italy, was appointed Poglavnik (leader) of an Ustaše-led Croatian state – the Independent State of Croatia (, NDH). The NDH combined almost all