Sometimes Americans think we have won a war, only to realize years or decades later that our victory was incomplete. Now we are facing an eruption of anger over a war we waged more than a century ago. Rarely has blowback from an overseas intervention come back to haunt us so long after the shooting stopped.

This unexpected challenge has emerged from the Philippines. The new president, Rodrigo Duterte, recently announced plans to pull his country out of America’s orbit and adopt an “independent” foreign policy. “I am anti-West,” he explained. “I do not like the Americans. It’s simply a matter of principle for me.”

Duterte’s grievance is rooted in history. Americans, he asserted, unjustly seized the Philippines in 1899, waged a horrific military campaign to suppress native resistance, and “have not even apologized to the Filipino nation.” He waved photographs showing bodies of Filipinos killed in that war.

Soon after Duterte made that startling speech, his foreign minister, Perfecto Yasay, went even further. In 1899, Yasay asserted, the United States “arrogated our victory in the struggle for freedom” and then used “invisible chains” to bind Filipinos into “shackling dependency.” Americans, he said, treat Filipinos as “little brown brothers not capable of true independence or freedom.” To escape from that humiliation, he concluded, the Philippines must end its “subservience to United States interests.”

Most Americans would have no idea what these new Filipino leaders are talking about. We forgot the Philippine War long ago. Filipinos remember it vividly. It stands with the horrors of Japanese occupation during World War II as one of their great national traumas. A very old debt is finally coming due. ...