Which of the following was NOT one of the four main causes for imperialism

This is the belief that a nation must develop and maintain a strong military force in order to pursue and defend its national interests.

How does a comet change when it comes close to the sun

How did the united states respond when north vietnam attacked a us warship and sent troops to south vietnam in the early 1960s? a.the united states declined to assist south vietnam against the north. b.us leaders authorized south vietnam to invade north vietnam. c.the president did not sign the gulf of tonkin resolution. d.congress authorized the president to escalate the conflict.