Opponents of the american acquisition of the philippines organized themselves into the

The answer you're looking for is The Anti-Imperialist League (established in 1898).  That gives you a clear indication that the United States' involvement in the Philippines was an act of imperialism.  During the late 19th century, imperialism was all the rage among European nations, scrambling to gain control of territories in Africa and Asia.  And the United States was not immune to this imperialist ambition.  The Anti-Imperialist League contended that a republican government (such as the United States) cannot be true to itself if it takes over control of territories without the consent of the people in those territories.