northern Greece and Turkey all the way to Iraq, and posed a threat to the Greek states. Attempts by the Greek city-states of Asia Minor to overthrow Persian rule failed, and Persia invaded the states of mainland Greece in 492 BC, but was forced to withdraw after a defeat at the Battle of Marathon in 490 BC. A second invasion followed in 480 BC. Despite a heroic resistance at Thermopylae by Spartans and other Greeks, Persian forces sacked Athens. Following successive Greek victories in 480 and 479 BC at Salamis, Plataea and Mycale, the Persians were forced to withdraw for a second time. The military conflicts, known as the Greco-Persian Wars, were led mostly by Athens and Sparta. However, the fact that Greece was not a unified country meant that conflict between the Greek states was common. The most devastating of intra-Greek wars in classical antiquity was the Peloponnesian War (431-404 BC), which marked the demise of the Athenian Empire as the leading power in ancient Greece. Both Athens and Sparta were later overshadowed by Thebes and eventually Macedon, with the latter uniting the Greek world in the League of Corinth (also known as the Hellenic League or Greek League) under the guidance of Phillip II, who was elected leader of the first unified Greek state in the history of Greece.
Following the assassination of Phillip II, his son Alexander III ("The Great") assumed the leadership of the League of Corinth and launched an invasion of the Persian Empire with the combined forces of all Greek states in 334 BC. Following Greek victories in the battles of Granicus, Issus and Gaugamela, the Greeks marched on Susa and Persepolis, the ceremonial capital of Persia, in 330 BC. The Empire created by Alexander the Great stretched from Greece in the west and Pakistan in the east, and Egypt in the south. Before his sudden death in 323 BC, Alexander was also planning an invasion of Arabia. His death marked the collapse of the vast empire, which was split into several