for the western way of life, our greatest hour was the greek defense against the persian forces at thermopylae and salamis 480BC, which arguably protected all of europe from being absorbed, and allowed western philosophy and politics to incubate.
darkest hour? that's a tough one. i'm gonna go with the hungarian revolt of 1956AD. the soviets came in, crushed the rebellion, and the world just watched.
:2 cents: