In 336 BCE, twenty-year-old Alexander III assumed the throne of Macedon after the assassination of his father, Philip II, by a royal bodyguard named Pausanias at the theater in Aegae. The army acclaimed Alexander as king without opposition. He moved quickly to eliminate rival claimants and secure his position, inheriting Philip's professional military force and his unfinished campaign against the Persian Empire. Over the next thirteen years, Alexander conquered territory from Greece to northwestern India.