Washington was not a fan of Imperialism. He believed that it could be damaging to America because it would get us into conflict that we were not strong enough to face at the time. Washington was in favor of the US keeping to ourselves and not being involved in foreign affairs.
During the 1900's Americans looked to expand the size of their nation. Some believed Imperialism would extend their control toward the Pacific Ocean. Things that influences American imperialism included the desire for military strength and the desire for new markets to sell goods.
Past American expansion including Manifest Destiny, can be considered similar to Imperialism because both were seeking economic expansion. Manifest Destiny was a more vague way of doing so because Americans believed they should explore coast to coast, all the way across the Atlantic and Pacific Ocean.
It created conflict among nations due to the desire for power and money. Imperial powers used colonies by taking advantage of their natural resources as strategy to develop in their own selfish ways.
Imperialism was very expensive. Having a large military force with quality weapons and coming up with enough invasion money is not easy. Colonizers spent more on military and warfare than anything else, which became very taxing for them and left them drained.
It divided nations. Although cultural diversity seems to be a good thing, it was not always good when countries had to break away due to dependence. The country was divided into stronger/wealthier nations which was unfair and went against basic equality morals of the US.
One of the main reasons America became more Imperialistic was due to economic desire to dominate. The desire to dominate arose from many different reasons, but I believe that the main reason was to benefit from other colonies goods. Imperialistic Americans sought to acquire raw materials for new markets with control over weaker nations. This is not justified. It was Un-American to decide to separate from each other and cruelly use others for what you can get out of them. America should be interested in seeking equality and teamwork to reach goals as one nation. One nation = one economy.