On June 20, 1898, during the Spanish–American War, the United States captured Guam. The existing Spanish garrison, including Governor Juan Marina, were taken as prisoners of war to Manila. The existing Spanish citizens of the island were also disarmed. Captain Henry Glass, the commander of the battle appointed Portusach as the acting-Governor of Guam, to serve until a formal military garrison could be sent. Portusach's only qualification for the position was that he was the only American citizen living on the island.