 Complete the following phrase:  The instability in Central America after the collapse of the Federal Republic of Central America forced Costa Rica to reform and modernize its army, especially after a threat of invasion from Nicaragua in 1848. With the arrival of Juan Rafael Mora Porras as president in 1849, Costa Rica acquired between 500-2000 1853 Enfield rifles in 1855. Later that year, the adventurer and mercenary William Walker imposed a military dictatorship in Nicaragua, reimposing slavery and threatening to conquer all of Central America. The 1853 Enfield rifle was used in the 