Campaign of 1856–57

William Walker's Conquest of Central America
Costa Rican and U.S. troops attacking William Walker at Rivas in 1856.
Date 1856–1857 Location Nicaragua Result Allied victory Filibuster defeat Surrender of William Walker to the U.S. Navy
Belligerents
Filibusters	Allied Central American Army (Ejército Aliado Centroamericano) * Nicaragua *  Costa Rica * Honduras * Mosquito Coast * Guatemala * El Salvador  United Kingdom (naval support) United States * Legitimistas (conservative party) * Democráticos (liberal party)
Commanders and leaders
William Walker Francisco Castellón Charles F. Henningsen Birkett D. Fry Collier C. Hornsby Domingo Goicouría Byron Cole	Ramón Belloso José Joaquín Mora Porras José María Cañas Tomás Martínez Guerrero Fernando Chamorro Alfaro Máximo Jerez Tellería José Víctor Zavala Charles Henry Davis
Strength
2,518 mercenaries	Unknown total * 2,500 troops * 4,000 troops
Casualties and losses
2,300 combatants dead (all causes)	2,000-3,000 combatants dead (all causes) ~5,000 wounded

Allied victory

The Filibuster War was a military conflict between filibustering multinational troops stationed in Nicaragua and a coalition of Central American armies.

In 1854, a civil war erupted in Nicaragua between the Legitimist party (also called the Conservative party), and the Democratic party (also called the Liberal party). The Democratic party sought military support from William Walker who, to circumvent American neutrality laws, obtained a contract from Democratic president President Castellón to bring as many as three hundred "colonists" to Nicaragua. Walker sailed from San Francisco on May 3, 1855, with approximately 60 men. Upon landing, the force was reinforced by 170 locals and about 100 Americans.

With Castellón's consent, Walker attacked the Legitimists in the town of Rivas, near the trans-isthmian route. He was driven off, but not without inflicting heavy casualties. On September 4, during the Battle of La Virgen, Walker defeated the Legitimist army. On October 13, he conquered the Legitimist capital of Granada and took effective control of the country. Initially, as commander of the army, Walker ruled Nicaragua through puppet President Patricio Rivas. U.S. President Franklin Pierce recognized Walker's regime as the legitimate government of Nicaragua on May 20, 1856.

Walker had scared his neighbors with talk of further military conquests in Central America. Juan Rafael Mora, President of Costa Rica, rejected Walker's diplomatic overtures and instead declared war on his regime. Walker sent Colonel Schlessinger to invade Costa Rica in a preemptive action, but his forces were defeated at the Battle of Santa Rosa in March 1856. In April 1856, Costa Rican troops penetrated into Nicaraguan territory and inflicted a defeat on Walker's men at the Second Battle of Rivas, in which Juan Santamaría, later to be recognized as one of Costa Rica's national heroes by burning the place were the Filibuster were staying. Walker set himself up as President of Nicaragua, after conducting an uncontested election. He was inaugurated on July 12, 1856, and soon launched an Americanization program, reinstating slavery, declaring English an official language and reorganizing currency and fiscal policy to encourage immigration from the United States of America.

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