Serbia & Montenegro
Radicalism had played a pivotal role in the birth and development of parliamentarism and the construction of the modern Serbian state leading to the Yugoslavian unification. The People's Radical Party formed in 1881 was the strongest political party and was in power in the Kingdom of Serbia more than all others together. The 1888 Constitution of the Kingdom of Serbia that defined it as an independent nation and formalized parliamentary democracy was among the most advanced in the entire world, due to Radical contribution, it's known as The Radical Constitution. In 1902 a crack had occurred in which the Independent Radical Party left and "the Olde" remained in the party, leading it to its considerable downfall and veering to the into conservatism. In the Yugoslavian kingdom, the Independent Radicals united with the rest of the Serbian opposition and the liberal and civic groups in the rest of the new country and formed the Yugoslav Democratic Party as the central, while several Republican dissidents formed a Republican Party. The NRS had promoted Serb nationalism and put itself as the defender of Serb national interests. Democrats and Radicals were the dominant political parties, especially since the exclusion of the Communists.
In Montenegro modelled a People's Party was formed in 1907 as the first political party and remained the largest in the period of country's parliamentary history until the Yugoslavian unification. Later a True People's Party was formed, which never got widespread popular support and whose bigger part had joined the original NS, but the difference was not ideological, but opposition and support of the Crown and, sometimes, in foreign relations to Serbia (the clubbists were the crown's dissidents and supporters of the people as well as Serbia as a regional power and brotherly ally; the rightists were generally anti-democratic and autocratic monarchist, whereas also distrustful to the Serbian government's acts on the national plan).
Read more about this topic: Radicalism (historical)