How did the USA betray Emilio?

After the U. S. declared war on Spain, Aguinaldo saw a possibility that the Philippines might achieve its independence; the U. S. hoped instead that Aguinaldo would lend his troops to its effort against Spain. He returned to Manila on May 19, 1898 and declared Philippine independence on June 12.

When it became clear that the United States had no interest in the liberation of the islands, Aguinaldo's forces remained apart from U. S. troops. On January 1, 1899 following the meetings of a constitutional convention, Aguinaldo was proclaimed president of the Philippine Republic. Not surprisingly, the United States refused to recognize Aguinaldo's authority and on February 4, 1899 he declared war on the U. S. forces in the islands. After his capture on March 23, 1901, Aguinaldo agreed to swear allegiance to the United States, and then left public life.