The Second Battle of Rivas occurred on 11 April 1856 between Costa Rican militia under General Mora and the Nicaraguan forces of William Walker. The lesser known First Battle of Rivas took place on 29 June 1855 between Walker's forces and the forces of the Chamorro government of Nicaragua.

At the time, a major trade route between New York City and San Francisco ran through southern Nicaragua. Ships from New York would enter the San Juan River from the Atlantic and sail across Lake Nicaragua. People and goods would then be transported by stagecoach over a narrow strip of land near the city of Rivas, before reaching the Pacific and being shipped to San Francisco. The commercial exploitation of this route had been attained from a previous Nicaraguan administration to Wall Street tycoon Cornelius Vanderbilt's Accessory Transit Company. Garrison and Morgan had wrested control of the company from Vanderbilt and then supported Walker's expedition. Vanderbilt spread rumors that the company was issuing stock illegally in order to depress its value, allowing him to regain controlling interest.