In 1873, the Spanish Constitutional Monarchy was replaced by a republican government. Although short-lived, the new Spanish Republic approved the abolition of slavery on the island on March 22, 1873. While the new law was considered a step forward by Puerto Rican liberals, it did not provide for immediate and total freedom of the island's black population. Efforts for further liberal reform on the island were aborted in 1874, when the Spanish Republic fell as the result of a military coup, leading to the return of the Spanish Monarchy. Spanish authorities once again appointed as governor José Laureano Sanz, who immediately overturned all established democratic practices. Thus, Puerto Rico returned to its colonial status, ruled by special laws dictated by a repressive ruler.
Between 1876 and 1898, the two liberal wings came together behind the idea of political autonomy, leaving behind the notion of assimilation with Spain. During the mid-1880s, they worked on a party platform calling for self government and renamed themselves the "Partido Autonomista Puertorriqueño" (Puerto Rican Autonomist Party). The pro-independence movement, meanwhile, planned several invasions from exile which never materialized for lack of funds and support.
Towards the end of the 1880s, the island's population suffered from a severe economic crisis. The local monopoly of Spanish merchants fueled resentment and led to the establishment of secret societies--organizations promoting the boycott of Spanish merchants and greater support for local business. There were many violent incidents against Spanish commercial establishments, particularly looting and arson. The government and its Civil Guard responded with a series of raids and imprisonments, applying severe torture measures which became known as "compontes". The social conditions of the island were also critical during this period. In addition to a lack of civil liberties, approximately 85 percent of the population remained illiterate. Malnutrition and extreme poverty were widespread throughout most of the countryside.
Puerto Ricans finally were granted self-government by Spain, when the "Carta Autonómica" (a form of constitutional autonomy) was approved by the Spanish Cortes in November 25, 1897. Nevertheless, by the time of the first elections in March 1898, tensions were already building up between Spain and the United States, and the short-lived self-government experiment came to an abrupt end one month later with the advent of the Spanish-American War.
The dawn of a new colonial era under the United States.
The strategic value of Puerto Rico for the United States at the end of the nineteenth century centered in economic and military interests. The island's value to US policy makers was as an outlet for excess manufactured goods, as well as a key naval station in the Caribbean. US Navy Captain Alfred T. Mahan became the leading strategist and advisor to his government during the 1880s. He joined the faculty of the US Naval War College in 1884 and became its president in 1886. Mahan formulated a strategic doctrine based on naval power as the main element of military supremacy. Thus, the strategic doctrine of the United States, until then focusing on ground warfare, was replaced by the primacy of naval power. US naval power in the hemisphere, resulting from the ascendancy of its naval technology at the time, thus became the strategic basis of US military doctrine and foreign policy during the late nineteenth century.
Mahan played a key role in the Spanish-American War, as a military strategist and close advisor to President McKinley throughout the conflict. Overall, the US war strategy called for a predominantly maritime conflict in which the newly upgraded US Navy could display its might.
During 1894 the first plans for a military conflict with Spain were formulated at the US Naval War College. In 1896, a formal war plan was developed by Lieutenant William W. Kimball, a naval intelligence officer at the War College. The stated objective was to 'liberate Cuba' from Spanish rule. The main theater of operations would be the Caribbean, focusing on the Cuban and Puerto Rican coastal regions, and the conflict would involve exclusively naval operations. According to this plan, US naval power would be employed against the Spanish Navy at those points where the enemy would face an equal or superior force.
Accordingly, the US Department of the Navy began operational preparations early in 1898. These took into consideration a wealth of intelligence reports on the weakening conditions of the Spanish forces. The mysterious explosion of the Maine battleship in the Havana harbor, killing some 300 US marines on February 15, 1898, was the turning point for the United States to start its war operations. On April 21st, President McKinley formally requested that the US Congress declare war against Spain. Although the US war effort had, in retrospect, its tactical and logistical faults, its unquestionable military superiority over Spanish forces led to a quick US victory.
The Spanish-American war lasted some four months. On May 1st, US forces destroyed the Spanish fleet in Manila Bay, the Philippines dealing a decisive blow to the Spanish armada. Given the weakness of the Spanish forces, the US then decided to expand its campaign, and bring in ground troops. It also changed its strategy for Cuba and planned for military operations against Havana, the island's capital city and key post of Spain in the Caribbean. US troops landed in Cuba late in June and on July 17 destroyed the Spanish fleet stationed in Santiago de Cuba Bay, thus securing total control of the waterways in the Caribbean. Following these events, President McKinley set forth the conditions for peace negotiations. The evacuation of Cuba by Spanish forces and its transfer to the United States was the prelude to imposition of order and formation of a stable government on the island. McKinley's second demand was the transfer of Puerto Rico from Spanish authorities to the United States without compensation.
Although Spanish surrender was certain at this point, the occupation of Puerto Rico followed in an effort to secure the US presence on the island prior to the initial discussions of a peace settlement. On July 18, General Nelson A. Miles, commander of the invading forces, received orders to sail for Puerto Rico. Some 18,000 US troops with a naval escort departed for Puerto Rico from Guantánamo Bay and the east coast of the United States. They landed at Guánica Bay on July 25, immediately moving to the city of Ponce and other towns located on the southern part of the island. The US troops then proceeded north towards San Juan, Puerto Rico's capital and the main military post of Spanish forces on the island. But before they could reach San Juan, Spain agreed on August 13th to sign a peace treaty with the United States, putting an end to all military hostilities.
President McKinley's conditions for a peace agreement prevailed throughout the peace negotiations and were finally ratified in the Treaty of Paris, signed on December 10, 1898. The formal transfer of Puerto Rico to the United States took two months, from August 12 to October 18, when the last Spanish troops sailed back to Spain and the US flag was raised in most public buildings on the island. A military government was established under the command of General John R. Brooke.
The Treaty of Paris gave the United States full control over all former Spanish military installations as well as some 120,000 acres of land formerly owned by the Spanish Crown on the island. The main military posts were located in the capital city of San Juan along with military bases in the towns of Cayey, Aibonito, Ponce, Mayagüez, Aguadilla and the adjacent island of Vieques. Puerto Rico remained under direct control of US military forces until the US Congress ratified the Foraker Law on April 12th, 1900, bringing a civilian government to the island.