Abercromby's fleet invades the island of Puerto Rico with a force of six thousand to thirteen thousand men, which includes German soldiers and Royal Marines and sixty to sixty-four ships, in what will be one of the largest British attacks on Spanish territories in the western hemisphere.

Fierce fighting continues for the next days.

Both sides suffer heavy losses.

On Sunday, April 30, the British cease their attack and begin their retreat from San Juan in what will be one of the worst defeats of the British Royal Navy for years to come.

Cholera spreads through Puerto Rico, claiming twenty-five thousand eight hundred and twenty victims, from November 10, 1855, to December 1856.

Cemeteries are expanded to allow for the burial of victims of cholera.

The struggle for sovereignty in Puerto Rico marks the last half of the nineteenth century.

A census conducted in 1860 reveals a population of 583,308.

Of these, 300,406 (51.5%) were white and 282,775 (48.5%) were persons of color, the latter including people of primarily African heritage, mulattoes and mestizos.

The majority of the population in Puerto Rico is illiterate (83.7%) and lives in poverty, and the agricultural industry—at this time, the main source of income—is hampered by lack of road infrastructure, adequate tools and equipment, and natural disasters, including hurricanes and droughts.

The economy also suffers from increasing tariffs and taxes imposed by the Spanish Crown.

Furthermore, Spain has begun to exile or jail any person who calls for liberal reforms.

The first political organizations on Puerto Rico are formed as two factions emerge in 1870.

The Traditionalists, known as the Partido Liberal Conservador (Liberal Conservative Party) are led by José R. Fernández, Pablo Ubarri and Francisco Paula Acuña and advocated assimilation into the political party system of Spain.

The Autonomists, known as the Partido Liberal Reformista (Liberal Reformist Party) are led by Román Baldorioty de Castro, José Julián Acosta, Nicolás Aguayo and Pedro Gerónimo Goico and advocate decentralization away from Spanish control.

Both parties will later change their names, to Partido Incondicional Español (Unconditional Spanish Party) and Partido Federal Reformista (Reformist Federal Party), respectively.

Political and social reforms occur in Puerto Rico toward the end of the nineteenth century, following the Grito de Lares revolt.

The Moret Law, giving freedom to slaves born after September 17, 1868 or over sixty years old, had been approved on June 4, 1870, due to the efforts of Román Baldorioty de Castro, Luis Padial and Julio Vizcarrondo; on March 22, 1873, the Spanish National Assembly officially abolishes, with a few special clauses, slavery in Puerto Rico.

Puerto Rico becomes a dependent United States Territory in 1898.