The chain of events leading to the formation of the Persian Empire can be traced to the collapse of Assyrian power at the end of the 7th century BCE. The Medes were major territorial beneficiaries and, after extending their sway through northern Persia and eastern Anatolia, in around 550 BCE their King Astyages attacked Cyrus who had united the Persians in Anshan. Cyrus prevailed, and went on to create the largest empire the world had yet seen, conquering Lydia (547 BCE), Babylon (539 BCE) before dying while campaigning in eastern Persia. He was an innovative and tolerant ruler, establishing an efficient provincial government of satraps, and efficient postal system, and was welcomed by both Babylonians and Jews as a liberator. His son, Cambysses II extended the empire into Egypt after victory at Pelusium (525 BCE). Darius the Great (r. 522–486 BCE) would campaign in India, and suffer insurrection in the west from the empire’s recurring irritant and ultimate nemesis, the Greeks.