The Serbian Radical Party, Croatian Peasant Party, and Democratic Party competed with and allied with a large number of other ethnic and sectarian parties, with no single party ever gaining a majority. The Serbian Radicals under Pasic, the strongest party in the country, drew backing from Serbia proper and advocated strong central control under Serbian leadership. The Croatian Peasant Party under Stjepan Radic dominated Croatia and campaigned for an independent Croatian state and agrarian socialism. The Democrats found support mostly from Serbs outside Serbia; after initially advocating centralism, they turned to an opposition agenda.

The Serbian-Croatian rivalry, which was a clash of uncompromising advocates of central rule versus regional autonomy, produced the main political conflict in Yugoslavia. In November 1920, voters chose delegates to a Constituent Assembly. The Radic party won nearly all Croatian seats but, adopting an obstructionist strategy that had been typical of Croatian politics under the Dual Monarchy, it boycotted the assembly. When other anticentralist groups left the assembly in 1921, the Serbian Radicals and Democrats won by default the opportunity to adopt a centralist constitution. This document provided some liberties but allowed little room for local initiative or popular democracy, and it gave non-Serbs inadequate legal expression of their discontent. Communists attempted to assassinate King Aleksandar the day after the constitution took effect, and murdered the interior minister a month later. The new Federal Assembly (Skupstina), then passed broad security laws to suppress the Communist Party, which had gained considerable support with worker groups and poor peasants in the south.

Radic campaigned at home and abroad for Croatian autonomy, even seeking support in the Soviet Union--a country Yugoslavia did not recognize. The Croatian Peasant Party boycott of the kup tina lasted until 1924, when a dissident coalition of Democrats, Slovenes, and Muslims forced the Serbian Radicals from power. King Aleksandar then appointed an anti-centralist prime minister. Charges of corruption and Radic's harsh criticism of the Serbian establishment undermined the new cabinet. The Radicals soon regained power, arrested Radic for sedition, and threatened to ban his party.

Political realities, including the threat posed by fascist Italy to Croatia, induced Radic in 1925 to strike a deal with Aleksandar to recognize the monarchy and to join a government coalition led by Pasic. This union lasted until a corruption scandal forced Pasic to resign in 1926. Thereafter, weak coalitions failed to maintain stability, the Croats returned to obstructionism, and floor debates in the Federal Assembly often became violent. In June 1928, a Montenegrin deputy shot Radic, who died two months later. Deputies from Croatia and Bosnia and Hercegovina soon left the assembly, demanding a federal state. Fearing anarchy, Aleksandar abrogated the constitution in January 1929, dissolved the Assembly, banned political parties, and declared a temporary royal dictatorship.

While the Serbian-Croatian conflict occupied center stage, an equally bitter conflict arose between the Serbs and the ethnic Albanians in Kosovo. Serbs consider Kosovo to be hallowed ground, but their exclusive hold on the region slipped during the Ottoman tyranny in the late seventeenth century, and many Serbs fled Kosovo for Habsburg protection. After the mid-eighteenth century, Albanians became a majority in Kosovo and began oppressing the Serbs that remained. Between 1878 and 1912, Serbs left Kosovo in large numbers; in 1920 Belgrade began a drive to resettle Serbs in the region. Coercion, illegal expropriation of Albanian-owned land, and forced deportations marred this campaign. When Albanians attacked Serbian settlements and government institutions, the police seized Albanian property, imprisoned families, and destroyed homes. The government adopted a similar policy in Macedonia.

Data as of December 1990