From Ohio History Central
In 1898, the United States declared war on Spain. The principal reason for war involved the sinking of the United States battleship Maine.
Tensions had existed between the United States and Spain for several years before the Spanish-American War. Throughout the 1890s, many Americans objected to Spain's treatment of the people of Cuba, a colony of Spain. For decades, Cuban revolutionaries had attempted to overthrow Spanish authority. The Spanish government in Cuba forced suspected revolutionaries into prison camps, among other tactics. Some American reporters—the yellow press—printed sensational stories regarding Spanish atrocities in Cuba. Many Americans firmly believed that the United States, the bastion of representative government, could not permit Spain's continued subjugation of the Cuban people.
Tensions between the United States and Cuba came to a boiling point in February 1898. President William McKinley, an Ohioan, had dispatched the Maine to Cuba, purportedly to protect American citizens in Cuba in case a war erupted between the Spanish and the Cubans. In February 1898, the Maine exploded, killing 260 American servicemen. The American people were convinced that the Spanish were responsible, although there was no clear evidence to prove this accusation. Most historians now believe that an accident occurred onboard of the ship. Somehow gunpowder, most scholars contend, ignited in the gunpowder room, causing the explosion. McKinley sent a declaration of war to the United States Congress, which approved the declaration on April 25, 1898, signaling the start of the Spanish-American War.