The southernmost area of the Caucasus. Long under a vague Turkish suzerainty, Armenia was conquered by the Russians during the 19th century. During World War I, Armenia was occupied by Turkish and German forces. Between May 1918 and December 1920, and again between February and April 1921, it existed as an independent republic, issuing its own stamps. In 1923, it joined the Transcaucasian Federation of Soviet Republics. Transcaucasian issues were soon superseded by those of the Soviet Union. With the breakup of the Soviet Union, Armenia again became an independent republic. A long-standing dispute with neighboring Azerbaijan over the enclave of Nagorno-Karabakh, a territory completely encircled by Moslem Azerbaijan but populated mostly by Christian Armenians, has led to hostilities between the two countries in recent years.