Question

What explains the aim of u.s foreign policy from 1900 until the outbreak of world war 1?

Answer 1

Theodore Roosevelt was president in 1900. His confident feeling that the US could fix the worlds problems was at the heart of his foreign policy.
Problems in Columbia? We'll fix that and recognize Panama as a country and get a canal built too.
Japan and Russia at war? TR will negotiate a peace treaty and win a Nobel Prize doing it. Problems in the Caribbean and Latin America? We got the Roosevelt Corollary to the Monroe Doctrine to fix you right up and keep European powers from messing with the hemisphere. We were the world's policeman, sorta.
President Taft kept up the same type of thing. But with less bluster. Taft focused more on protecting American business. "Dollar Diplomacy". The policeman who knows who is paying the bills.
Wilson was elected on the idea of keeping us out of WWI. But he continued the intervention, especially locally. He sent General Pershing and troops into Mexico after Pancho Villa. Never caught him, but it was pretty much the US just going into another country to solve a problem. Before WWI started US troops were stationed in Mexico, Nicaragua, and Cuba.
Wilson also got involved in East Asia because of the growing Japanese empire.
When he addressed the nation about changing the his stance on WWI, he explained that the US would make this a war to end all wars and make the world save for democracy.