in the late 1800s, imperialist countries often used their colonies as; a key factor of the empires the united states and european countries built in the late 1800s was:; why did the united states establish the open door policy?; in the 1800s, what new technology helped nations build and maintain their empires?; what was the main way in which imperialist nations protected their colonies and trade in the 1800s?; in the late 1800s, western nations generally believed the peoples of africa and asia; anti-imperialist efforts in the late 1800s led the us to focus its foreign policy on; how did the us improve working conditions during the building of the panama canal?