The ancient Armenians were conquered by the Medians and then the Persians in the seventh century B.C. Armenia was conquered by Alexander the Great in the fourth century B.C., and was subsequently dominated by the Seleucid Empire, which ruled it indirectly through two separate satrapies. In 94 B.C., Tigranes the Great united the two kingdoms under his rule and asserted his independence from Seleucid rule.
During the Third Mithridatic War, Tigranes fought on the side of Mithridates, and invaded Mesopotamia, Asia Minor and Syria. In 69 B.C., he was defeated by Pompey the Great, and lost the lands he had conquered during the war. Under the terms of the peace treaty, Armenia became a client kingdom of Rome.
Over the ensuing centuries, Armenia strove to maintain neutrality in the struggles between Rome and Parthia, though it could not resist getting involved occasionally. Despite both powers' efforts to dominate the country, neither succeeded for long due to the remoteness of the region and the difficulty of mastering its mountainous terrain. During the Third Mithridatic War, Roman efforts to conquer Armenia bogged down in a drawn-out guerrilla war, and Rome was forced to acknowledge Armenian independence. Rome again attempted to rule Armenia briefly from 114 to 117 A.D., but was forced to withdraw. The Sassanid Persians tried to conquer it in the third century without any better success.
The King Tiridates III adopted Christianity as Armenia's state religion in 303 A.D. Despite subsequent conquests by Muslim Arabs, Turks, and Persians, the region has retained its distinct sense of nationality and its Christian identity to this day.