1: Their particularly brutal slavery is why they had to militarize their citizens (meaning a different thing in those days btw), not why they could.
2: The Greek alliance was expecting Thermopylae to hold indefinitely, the fortified position was considered impregnable. What was actually impressive was Persia defeating it, and the allied Greek navy fighting twice its number while inflicting decisive casualties, withdrawing in order, and then crushing the Persian fleet at Salamis and forcing the Persian army to withdraw or starve.
Although the fleet numbers are generally assumed to be lies and historians generally think the fleets were roughly even at Thermopylae.
1: Their particularly brutal slavery is why they had to militarize their citizens (meaning a different thing in those days btw), not why they could.
2: The Greek alliance was expecting Thermopylae to hold indefinitely, the fortified position was considered impregnable. What was actually impressive was Persia defeating it, and the allied Greek navy fighting twice its number while inflicting decisive casualties, withdrawing in order, and then crushing the Persian fleet at Salamis and forcing the Persian army to withdraw or starve.
Although the fleet numbers are generally assumed to be lies and historians generally think the fleets were roughly even at Thermopylae.