Walker is hardly an unknown figure. When the United States was supporting the Nicaraguan Contras, Walker was frequently pointed to as a past example of American imperialism.
But a new book, "Tycoon's War," by historian Stephen Dando-Collins, brings to light an aspect of Walker's career that has not been well appreciated: his conflict with America's richest man, Cornelius Vanderbilt.
Walker was a fascinating figure. Born in 1824, he was raised in Nashville. He mastered Greek and Latin by age 12 and was admitted to the University of Nashville, from which he graduated summa cum laude two years later.
At 14 he enrolled in medical school and earned his M.D. at 18. He then went to Europe to further his studies.
After his return to the United States, devastated by his inability to save his ailing mother's life, he abandoned medicine and earned a law degree in two years.
He helped found a liberal newspaper in New Orleans, where he took on corrupt politicians, judges and police, and editorialized against slavery.
The shock of his fiancee's death in a cholera epidemic caused Walker to intensify his campaign against city corruption. That resulted in two duels and eventually led to the newspaper's demise, after which Walker went to California.
Upon arrival in 1850, he began writing for the San Francisco Herald and again attacked rampant corruption.
Walker also believed in the Manifest Destiny doctrine. Walker put his politics into practice in 1852, when he put together an expedition to try to establish an American colony in lower California and Sonora. With no military experience, he led his "filibustering" expedition and in 1853 captured the governor of La Paz and waited for reinforcements to arrive to help him secure the region.
Walker's invasion shook the Mexican government, which feared he was backed by America, and they hastily signed the Gadsden Purchase Treaty on Dec. 31, 1853. Upon doing so, American authorities declared Walker to be in violation of the Neutrality Laws.
Walker surrendered himself and was arrested for violating the Neutrality Laws. He delivered such a performance in the courtroom that the jury found him not guilty.
Walker returned to the newspaper business and was hired as editor of the San Francisco Commercial-Advisor.
What does this have to do with Vanderbilt, who was the Bill Gates of his time?
Vanderbilt and other American business tycoons were already developing commercial interests in the region. The publisher of the Commercial-Advisor tried to persuade Walker to raise a group that could invade Nicaragua, a nation wrapped in continuous civil war, and bring it under American control. Walker refused, saying he would have to be invited by one of the parties at war in contractual form, which would provide him a legal ground from where he could operate. The publisher soon delivered a contract from the Liberal Party in Nicaragua asking for his help in fighting the Conservatives.
With the same strict discipline he used in his Sonora campaign, Walker and 58 men sailed in May 1855 for Nicaragua and made their way to the revolutionary capital of Leon. Walker's reputation had preceded him and he was well received. He and his men captured Granada. Their fighting abilities and Walker's leadership defeated numbers that were as much as 10 to one.
His story captured world attention. He had brought an element of peace to the war-ravaged country and hoped the changes he enacted would help bring the entire Central American region under American control.
In the new revolutionary government that formed, he was made commander in chief of the Nicaraguan army. As such, he controlled Nicaragua. In 1858 minor breakdowns and uprisings led to the collapse of the government, and in Walker's re-establishment of it he was elected president. Walker's government was recognized by the U.S. government under President Franklin Pierce, and friendly relations were established.
Walker was so popular, he was able to recruit thousands of Americans into his private army.
But unknown to Walker, however, was the fact that he had got caught between Vanderbilt and his competitors, who were both trying to use Walker's success to further establish their wealth and control over Central American resources.
Vanderbilt was not a man to confine himself to the legal process. As he wrote to his former associates, "Gentlemen, you have undertaken to cheat me. I won't sue you, for the law is too slow. I'll ruin you. Yours truly, Cornelius Vanderbilt."
The gold rush was heating up in California, and Vanderbilt wanted to shuttle passengers from the East Coast to the West. Without a railroad or a Panama Canal, the quickest way to do this was to send them around the southern tip of South America.
Vanderbilt had another idea: send boats through the Caribbean to Nicaragua, get on the San Juan River at Greytown, follow the San Juan to Lake Nicaragua, use mules to cover a small strip of ground between the Lake and San Juan Del Sur, and dump them out onto the Pacific. From there, the trip to California was relatively short. In a nutshell Vanderbilt needed Nicaragua, Walker's territory, to make his money.
Walker's men seized the steamship line owned by Vanderbilt and started making deals that would be beneficial to the Nicaraguan government. This angered Vanderbilt, who began financing rebel forces in Costa Rica to overthrow Walker.
Subsequently President James Buchanan, who promised in his platform to aid the Central American causes, sided with Vanderbilt. Following various battles, Walker was forced to surrender and return to America.
In 1859 British colonists on the Honduran island of Roatan approached Walker to help them establish a government to preserve Democratic rule after the British pulled out its forces. Walker and his force arrived, but the British government responded by sending in British marines and forced him to surrender. He was then handed over to Honduran authorities, who executed him.
(U.S. Navy veteran David Isenberg is a military affairs analyst. He is an adjunct scholar with the Cato Institute, a correspondent for Asia Times and the author of a forthcoming book, "Shadow Force: Private Security Contractors in Iraq." His "Dogs of War" column, analyzing developments in the private security and military sector, appears every week.)