It's a bit more complex. There had been an independence movement in the Philipines, led by Emilio Aguinaldo and others. It also fought the Spanish , at the same time the US was involved in the Spanish American War. When the US defeated Spain ( the Battle of Manilla Bay, in August of 1898) President McKinley was faced with a choice of handing over the country to Aguinaldo or taking control. Handing it over would go along with previous US rhetoric about liberating the Filipinos from tyranny, taking control would give the US a very handy coaling station for its Navy. McKinley was a ditherer, and he dithered until December, when a deal was struck with Spain ( $20 million for the whole country was, even back then, almost nothing- it was reimbursing Spain for buildings, port facilities... ). Helping him decide was the presence of German battleships in Philippine waters, and the probability that, if the US didn't take possession, others would. But US hypocrisy rankled many- journalist Peter Finley Dunne called it " hands across the water, and into someone's pocket".

And the $20 million didn't keep the US from soon getting into a miserable guerrilla war with the disappointed Filipino insurgents. That lasted for years, cost much more - requiring a US army of some 124,000 75,000. It killed some 6,000 US soldiers, wounded thousands more, killed 200,000 or more civilians- and is now almost completely forgotten in the US.