During the Philippine-American war. 1899-1902 Gore Vidal thought so:
"The comparison of this highly successful operation with our less successful adventure in Vietnam was made by, among others, Bernard Fall, who referred to our conquest of the Philippines as "the bloodiest colonial war (in proportion to population) ever fought by a white power in Asia; it cost the lives of 3,000,000 Filipinos." (cf. E. Ahmed's "The Theory and Fallacies of Counter-Insurgency," The Nation, August 2, 1971.) General Bell himself, the old sweetheart, estimated that we killed one-sixth of the population of the main island of Luzon—some 600,000 people."
Others reduce the Philippine "Genocide" to 1.4 million:
"EXCEPT during the sixties when the Filipino-American War of 1899-1902 was referred to as “the first Vietnam,” the death of 1.4 million Filipinos has been usually accounted for as either collateral damage or victims of insurrection against the imperial authority of the United States. The first Filipino scholar to make a thorough documentation of the carnage is the late Luzviminda Francisco in her contribution to The Philippines: The End of An Illusion (London, 1973)."
Population of the Philippines*
1887: 6,584,727 (est. 500,000 non-Christians)
1899: 7,303,311 (est. 600,000 non-Christians)
1903: 7,635,426 (647,000 Non-Christians)
* = Sources: Philippine Statistics board; 1903 and 1918 Philippine census.
Plus 1903 census shows a overall ratio of males/females of 50/50. War and "Genocide" in response to Guerrilla warfare usually kills many more men than women, so you'd expect the ratio of young men/young women to be highly unbalanced *after* the war. And also see a large number of widows. Instead you see the following:
1903 Census - Widows - 330 thousand
1918 Census Widows - 340 thousand
1903 Census - Men 18-29 - 675 thousand
1903 Census - Female 18-29 - 800 thousand
1903 Census Males 30-39 - 490 thousand
1903 Census Females 30-39 - 450 thousand