"Well I Hardly Know Which To Take FIrst", "A Lesson for Anti-Expansionists" and "What Will He Do?" reveal the conflict between expansionists and anti-expansionists. The United States stood to gain from the possession of the Philippines, which provided an entry-point into Asia, which would provide new markets for American products and present opportunities for economic growth. Puerto Rico provided a strategic location from which to protect the Panama Canal and to stage any forays into South America.
With the Monroe Doctrine as an anti-imperialist document, the United States' evolution into a colonial power threatened to undermine the way the world would view it. The United States managed to find a way around this by exerting economic influence over the Carribbean and South America, rather than by occupation and incorporation. Cuba and the Philippines were both eventually granted independence, while Guam and Puerto Rico remain "freely associated".
However, the case of Puerto Rico's commonwealth status is an eye sore on the face of American politics. The Puerto Rican people were granted citizenship and drafted into service for World War I and while Puerto Ricans have served faithfully and exceptionally in every American war since then, the land of Puerto Rico itself is still considered foreign and outside of the United States. This equates to a modern form of colonialism, where the people have been incorporated into "America" and yet the land is not treated as an equal State of the Union.