In the era of the expansion of the United States, driven by the doctrine of "manifest destiny", Walker organized unauthorized military expeditions into Mexico and Central America with the intention of establishing colonies.

Walker then went to Nicaragua in 1855 as leader of a mercenary army employed by the Nicaraguan Democratic Party in its civil war against the Legitimists.

[1] Walker's regime was recognized as the legitimate government of Nicaragua by US President Franklin Pierce, and it initially enjoyed the support of some important sectors within Nicaraguan society.

As ruler of Nicaragua, Walker re-legalized slavery, although this measure was never enforced, and threatened the independence of neighboring Central American republics.

[3] Walker then tried to re-launch his filibustering project and in 1860 published a book, The War in Nicaragua, which cast his efforts to conquer Central America as tied to the geographical expansion of slavery.

In that way, Walker sought to gain renewed support from pro-slavery forces in the Southern United States on the eve of the American Civil War.

The same year, Walker returned to Central America but was arrested by the Royal Navy, who handed him over to the Honduran government, which executed him.

Walker then conceived the idea of conquering vast regions of Central America and creating new slave states to join those already part of the Union.

Walker tried a number of times to shoot his weapon, but he failed to land even a single shot and Graham was left unscathed.

[21] Fearful of attacks by Mexico, Walker moved his headquarters twice over the next three months, first to Cabo San Lucas, and then further north to Ensenada to maintain a more secure base of operations.

[10] Lack of supplies, severe aridity of Baja California and strong resistance by the Mexican government quickly forced Walker to retreat.

[20] Back in California, Walker was indicted by a federal grand jury for waging an illegal war in violation of the Neutrality Act of 1794.

People and goods were then transported by stagecoach across a narrow strip of land near the city of Rivas, before reaching the Pacific and ships to San Francisco.

The commercial exploitation of this route had been granted by Nicaragua to the Accessory Transit Company, controlled by shipping magnate Cornelius Vanderbilt.

[28] Besides Henningsen, three members of Walker's forces who became Confederate officers were Birkett D. Fry, Robert C. Tyler, and Chatham Roberdeau Wheat.

[31] Walker's actions in the region caused concern in neighboring countries and potential U.S. and European investors who feared he would pursue further military conquests in Central America.

[33] Concerned about Walker's intentions in the region, Costa Rican President Juan Rafael Mora Porras rejected his diplomatic overtures and began preparing the country's military for a potential conflict.

[34] Walker organized a battalion of four companies, of which one was composed of Germans, a second of Frenchmen, and the other two of Americans, totaling 240 men placed under the command of Colonel Schlessinger to invade Costa Rica in a preemptive action.

Both the nickname by which Hondurans are known today, Catracho, and the more infamous nickname for Salvadorans, "Salvatrucho", are derived from Xatruch's figure and successful campaign as leader of the allied armies of Central America, as the troops of El Salvador and Honduras were national heroes, fighting side by side as Central American brothers against William Walker's troops.

By establishing control of this bi-national river at its border with Nicaragua, Costa Rica prevented military reinforcements from reaching Walker and his Filibuster troops via the Caribbean Sea.

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 emigration from the United States.

Nevertheless, Walker's army was weakened by massive defections and an epidemic of cholera and was finally defeated by the Central American coalition led by Costa Rican President Juan Rafael Mora Porras (1814–1860).

On October 12, 1856, Guatemalan Colonel José Víctor Zavala crossed the square of the city to the house where Walker's soldiers took shelter.

[41] On December 14, 1856, as Granada was surrounded by 4,000 troops from Costa Rica, Honduras, El Salvador, and Guatemala, along with independent Nicaraguan allies, Charles Frederick Henningsen, one of Walker's generals, ordered his men to set the city ablaze before escaping and fighting their way to Lake Nicaragua.

[44] On May 1, 1857, Walker surrendered to Commander Charles Henry Davis of the United States Navy under the pressure of Costa Rica and the Central American armies and was repatriated.

[46] Rather than return him to the U.S., for reasons that remain unclear, Salmon sailed to Trujillo and handed Walker over to the Honduran government along with his chief of staff, Colonel A. F. Rudler.

Senator John J. Crittenden proposed that the 36°30' parallel north be declared as a line of demarcation between free and slave territories, some Republicans denounced such an arrangement, with New York congressman Roscoe Conkling saying that it "would amount to a perpetual covenant of war against every people, tribe, and State owning a foot of land between here and Tierra del Fuego".

To this day, a sense of Central American "coalition" among the nations of Costa Rica, Honduras, El Salvador, and Guatemala, along with independent Nicaraguan allies, is remembered and celebrated as a unifying shared history.

The villain of the Nantucket series, by science fiction writer S. M. Stirling, is a 20th-century American mercenary named William Walker, who is time-displaced from 1998 CE to 1250 BCE.

Walker demonstrates a similar personality to his historical namesake, leading a filibuster force to Mycenaean Greece and initiating a version of the Trojan War with firearms.