In 1895, a new war of independence began in Cuba, the third such conflict in 30 years. Cuba was supported by the United States for reasons of economic interest and investments in the sugar industry. In Puerto Rico also, there were many demonstrations of solidarity with its island neighbor, and dozens of Puerto Ricans, including General Rivera and the poet Pachín Marín Ruíz, went to Cuba to fight for the Cubans' cause.

Spain sent a force of thousands of soldiers to put down the Cuban rebellion and to defeat the rebels. The Military Governor of Cuba, General Valeriano Wyler, known in the North American press as "the butcher", decided to round up all opponents of Spanish rule and imprison them in camps, where they lived in terrible and inhuman conditions. These concentration camps were the subject of many press articles in the United States, especially in New York, and provoked an antagonism towards Spain on the part of the American people. Because of the heavy fighting, the warship Maine of the United States Navy was despatched to Havana to protect American citizens and its interests in Cuba.

On February 15, 1898, the situation worsened when the Maine exploded mysteriously in the Bay of Havana, killing 258 American sailors. The exact cause of the explosion has never been discovered. The United States blamed the Spanish Government for the deaths and the loss of the ship and demanded that Spain withdraw immediately from Cuba and its other colonies. This demand caused the breaking of diplomatic relations between the two countries, and Spain declared war on the United States on April 24. Thus began the conflict known as the Spanish American War.

The United States learned that a fleet had left Spain en route to the Caribbean and decided to despatch a fleet of its own to engage it. Spain had only two friendly ports in the Caribbean which could offer its fleet security and coaling facilities, namely, San Juan in Puerto Rico and Santiago de Cuba. As San Juan was the nearest to Europe on the Spanish fleet's route, it was logical to send the American fleet there.

The reality of war came to Puerto Rico on May 12, when San Juan awakened to the sound of the guns of an American fleet of 11 warships under the command of Admiral William P. Sampson.

The purpose of the four hour bombardment was not to destroy the fortifications, but to ascertain if the Spanish fleet was resupplying in the bay of San Juan, for this reason, the Castles sustained only minor damage.

On July 25, 1898, General Nelson Miles disembarked an invasion force at Guánica, in the south west of the island. As the American troops

were advancing towards San Juan, Spain surrendered and later signed an armistice in August of 1898. In October of the same year, the defenses of San Juan were officially handed over to the United States Army.

Under the Treaty of Paris, signed in December, 1998, Article 2:

"Spain cedes to the United States the island of Puerto Rico, together with the remaining territories under Spanish sovereignty in the Antilles, and the island of Guam....."

So ended the war and four centuries of Spanish domination. It also began a new chapter in the history of the Castles of Old San Juan.