Soviet Troops (file photo)

The Mighty: There is no greater historical example of an unstoppable force hitting an immovable object than the Soviet invasion and occupation of Afghanistan. Afghanistan is a mountainous, landlocked, harsh country that makes it very difficult for a great power to bring the full might of that power to bear against the locals. Naval forces are out and, in some area, so is air support. The harsh climate and vast nothingness and remotely populated areas makes supply lines difficult to establish and even harder to defend. But the Soviet Union opted to try anyway, invading in force in 1979. Click here to read more (external link).