Alexander I  ( born December 4 [December 16, New Style], 1888 , Cetinje, Montenegro [now in Yugoslavia]—died Montenegro—died October 9, 1934 , Marseille, France )  king of the Kingdom of Serbs, Croats, and Slovenes (1921–29) and of Yugoslavia (1929–34), who struggled to create a united state out of his politically and ethnically divided collection of nations.

The second son of Peter Karadjordjević (Karageorgević, or Karaðorðevići)—king of Serbia 1903–18 and king of the Serbs, Croats, and Slovenes 1918–21—and Zorka of Montenegro, Alexander spent his early youth in Geneva with his father, then in exile from Serbia, and in 1899 went to St. Petersburg, where he entered the Russian imperial corps of pages in 1904. In 1909, however, when his elder brother renounced his right of succession, Alexander, having become heir apparent, joined his family in Serbia.

A distinguished commander in the Balkan Wars of 1912–13, Alexander was appointed regent of Serbia by the ailing King Peter (June 24, 1914) and during World War I served as commander in chief of Serbia’s armed forces, entering Belgrade in triumph on October 31, 1918. As prince regent, he proclaimed the creation of the Kingdom of Serbs, Croats, and Slovenes on December 1, 1918.

The instability of the new state was demonstrated by an attempt on his life on the day (June 28, 1921) that Alexander swore an oath to uphold the constitution. Nevertheless, on August 16 he succeeded his father as king and on June 8, 1922, he married Marie, a daughter of Ferdinand I of Romania. Later Alexander attempted to consolidate the rival nationality groups and political parties into a unified state.

During the 1920s mounting political tensions forced numerous changes in government ministers and culminated in the murder of several Croat deputies by a Montenegrin deputy during a Skupština (parliament) session (June 20, 1928). The Croat members then withdrew from the Skupština; and, because Alexander could neither negotiate a satisfactory compromise for restructuring the body nor form an effective government, he dissolved it, abolished the constitution of 1921, and established a royal dictatorship (January 6, 1929).

Continuing his efforts to unify his subjects, Alexander changed the name of the country to Yugoslavia (October 3, 1929), outlawed all political parties based on ethnic, religious, or regional distinctions, reorganized the state administratively, and standardized legal systems, school curricula, and national holidays. He also tried to relieve the peasantry’s financial difficulties, eased relations with Bulgaria (1933), and engaged Yugoslavia in the Little Entente (with Czechoslovakia and Romania) and the Balkan Entente, an alliance with Greece, Turkey, and Romania (1934).

In the process Alexander created a police state that required military support for survival. When a new constitution was promulgated (September 3, 1931), the dictatorship was, in effect, given a legal foundation. Although Alexander’s acts were at first well received, demands for a return to democratic forms intensified by 1932, when a major economic crisis resulting from the worldwide depression added to political dissatisfaction. As a result, Alexander seriously considered restoring a parliamentary form of government; but before he was able to do so, he was assassinated by an agent of Croatian separatists while making a state visit to France.