The U.S. battleship USS "Maine" was sent to protect American interests, but soon after arrival, it exploded in Havana harbor and sank quickly, killing nearly three-quarters of the crew. The cause and responsibility for the sinking of the ship remained unclear after a board of inquiry. Popular opinion in the U.S., fueled by an active press, concluded that the Spanish were to blame and demanded action. Spain and the United States declared war on each other in late April 1898. Over the previous decades, five U.S. presidents—Polk, Pierce, Buchanan, Grant, and McKinley—had tried to buy the island of Cuba from Spain.