First Battle of Rivas

The First Battle of Rivas occurred on June 29, 1855 as part of the struggle to resist William Walker, an American filibuster, adventurer, and soldier of fortune who arrived in Nicaragua with a small army of mercenaries in June 1855 in support of the democratic government of General Castellon in the Nicaraguan civil war.

His army with local support was able to defeat the Legitimist party (Aristocratic) and conclude the Nicaraguan civil war.

Background
A civil war was then raging in the Central American republic of Nicaragua. The Liberal party (Democratic) and the Legitimist party (Aristocratic), were constantly warring with one another as they continually tried to gain political control through violent means. “During a period of six years Nicaragua had had no fewer than fifteen presidents”

William Walker
William Walker was part of a failed attempt to conquer the Mexican territories of Baja California and Sonora. Back in California, he was put on trial for conducting an illegal war. In the era of Manifest Destiny, his filibustering project was popular in the southern and western United States and the jury took eight minutes to acquit him.

While in America working as an editor at a local paper, Walker came to know Byron Cole. Cole had lived for several years in Central America, including Nicaragua. He convinced Walker that because of the ongoing civil war in the country, Nicaragua would be the perfect place to start an empire. Walker agreed and sent Cole to Nicaragua on August 15, 1854 to negotiate with the local parties. Cole was able to enter into an agreement with revolutionary Castellon whereby Walker was authorized to engage three hundred men for military duty in Nicaragua. The men would be paid a monthly wage and a certain amount of land after the campaign finished.

When Cole returned to America, Walker balked at the terms as it would violate the Act of Congress of 1818 commonly known as the neutrality law. However he told Cole that if he returned to Nicaragua and was able to get from Castellon a contract of colonization, Walker could act. Cole sailed a second time to meet Castellon and was able to get the colonization grant and an act stating that Walker's men would be guaranteed forever the privilege of bearing arms.

Walker sailed from San Francisco on May 3, 1855 with 57 men, to be reinforced by 170 locals and about 100 Americans upon landing, including then well-known explorer and journalist Charles Wilkins Webber.

First Battle of Rivas
On September 1, Walker defeated the Nicaraguan national army at La Virgen and, a month later, conquered the capital of Granada and took control of the country.