By 430 B.C., the Greeks could no longer live in peace with one another. Athens and Sparta were engaged in a conflict known as the Peloponnesian War. Though Sparta ultimately prevailed, all of Greece was weakened by the war. In 338 B.C, they were invaded by the Macedonians, a mountain tribe led by their king, Philip. Philip’s goal was to unite the Macedonians and the Greeks in one army to defeat the Persians, but he was assassinated before he could succeed. His son, Alexander, inherited the kingship of Greece and Macedonia at 20 years old. Alexander was exceptionally ambitious, handsome, and intelligent. His tutor was Aristotle, one of the greatest thinkers in Western history. Alexander was as popular with the Greeks as with the Macedonians, and he soon marched on the Persians. He began in Asia Minor, where he defeated the large but leaderless Persian army. Before marching on Persia directly, Alexander attacked and ultimately conquered the rear Persian provinces of Egypt and Phoenicia. In Egypt, he founded the city of Alexandria, which became one of the most powerful cities in the world. He was now king of Egypt, Greece, Phoenicia, Palestine, Babylonia, Assyria, Asia Minor, and Persia.