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A group of American mercenaries led by William Walker set sail from San Francisco to conquer Nicaragua.

Historical image related to A group of American mercenaries led by William Walker set sail from San Francisco to conquer Nicaragua. from May 3, 1855

Mercenary

Soldier who fights for hire

A mercenary is a private individual who joins an armed conflict for personal profit, is otherwise an outsider to the conflict, and is not a member of any other official military. Mercenaries fight for money or other forms of payment rather than for political interests.
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William Walker (filibuster)

American physician, lawyer, journalist, and mercenary (1824–1860)

William Walker was an American physician, lawyer, journalist, and mercenary. 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…
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Filibuster War

1856–57 invasion of Nicaragua by American filibuster William Walker

The Filibuster War, also referred to the Walker affair and known in Costa Rica as the National Campaign of 1856–1857, was a war fought in Central America between 1855 and 1857. The militaries of Costa Rica, El Salvador, Guatemala, Honduras, and Nicaragua established the Allied…
Source: Wikipedia (CC BY-SA)