The U.S. wanted to annex Hawaii because of their resources. The U.S. wanted to trade and spread Christanity. Queen Liliuokalani wanted Hawaii Hawaiians, so Stanford Dole and U.S. Minister, John Stevens, planned a surprise military invasion without president Cleveland knowing. President Cleveland did not support this, but president McKinley made Hawaii a state anyways.
The U.S. sent the USS Maine to Havana. After a while, the ship blew up. Many journalists blame this on Spain and gained support from Americans to start a war. This cause the Spanish-American war.
United States in 1853 sent a steam-powered fleet to Japan to force open trade with outside nations (lead by Commodore Matthew Perry). The force convinced Japan to work toward industrialization. Japan rapidly modernized, eventually leading to the Russo-Japan War.
In china, spheres of influence had divided the country into areas controlled by European nations. The U.S. was not included in this division. This caused the Open Door Policy (U.S. Plan providing each nation with equal opportunity to trade within China).
American and British leaders and businessmen wanted to ship goods quickly and cheaply between the Atlantic and Pacific coasts. America paid $10 million up front and paid $250,000 annually. After years of US control and revolts between Panama and Columbia, the US finally signed a treaty, which gave control back to Panama.
After the victory of the Spanish-American War, Spain sold the Philippines to the US. This lead to Guerilla wars lead by Emilio Aguinaldo ( this lasted three years ). America Eventually granted Indepenence in 1946, after huge loses of men.