Why were the spartan soldiers willing to sacrifice themselves at thermopylae?

Why did the united states become involved in the soviet-afghan war? the united states wanted access to the afghan oil fields. the united states wanted to retaliate against the soviet boycott of the 1984 olympics in los angeles. representative charlie wilson convinced congress to fund afghan resistance to soviet influence. president ronald reagan wanted to force the soviets to withdraw from afghanistan.

Which would be good historical evidence when studying manifest destiny?

Which is true about the monroe doctrine?