The main justification of US taking Philippines under its possession was Treaty of Paris, which was signed after the end Spanish-American war in 1898 which stated that Spain should:
-Give up all rights to Cuba (Teller Amendment and Platt Amendment).
-Surrender Puerto Rico and give up its possessions in the West Indies.
-Surrender the island of Guam to the United States.
-Surrender the Philippines to the United States for a payment of twenty million dollars.
But Philippines obviously didn’t submit to the US government and revolted against them which unfortunately led to the deaths of an estimated 200k to 250k civilians.
One Filipino writer wrote:
“Now here is a unique spectacle – the Filipinos fighting for liberty, the American people fighting to give them liberty”