The Persian Empire originated in 550 BC under the rule of Cyrus the Great, who conquered surrounding kingdoms and established an empire spanning 2000 miles through military prowess but also tolerance of local customs. The empire reached its height under Darius I in the 5th century BC, incorporating governance structures like satraps and a royal road system. However, defeats against the Greeks in the Persian Wars weakened the empire, and it was eventually conquered by Alexander the Great in the 4th century BC due to military, leadership, social, and economic problems including overtaxation, weak rulers, and satraps declaring independence.