The Pacific island captured by the United States from Spain without resistance in June 1898 was Guam. The bloodless capture occurred during the Spanish-American War, when the protected cruiser USS Charleston arrived off the island on June 20.
Guam's small Spanish garrison had not yet learned that war had begun. Spanish officials initially believed the American ships might be firing a salute and had no realistic ability to oppose the operation. After American officers came ashore, the Spanish authorities and 54 soldiers surrendered, and the American flag was raised over Santa Cruz Fort.
Guam's capture was strategically important because the island offered the United States a naval position in the western Pacific. The United States retained control after Spain formally ceded Guam in the December 1898 Treaty of Paris. Guam was therefore not merely occupied temporarily during the fighting; it became an American possession and later a major U.S. military hub.