Hessians were German mercenary soldiers hired by the British Empire during the American Revolution. Approximately 30,000 Germans fought for the British during the Revolution, and since half of them came from the Hesse region, the name "Hessians" was born.
In the 18th century, Germany was loose confederation of small states. A number of these states had professional armies that could be hired out. Entire units, complete with their own regimental colors, uniforms, weapons and officers were shipped to America to fight for the British. Landgrave Frederick II of Hesse-Kassel sent the largest of these units, but other units came from Hesse-Hanau, Brunswick-Wolfenbüttel, Ansbach-Bayreuth and Anhalt-Zerbst.
The first 18,000 Hessian troops arrived in America in 1776, landing at Staten Island and were first used at the Battle of Long Island, a major American defeat. Many American Loyalists were turned away from supporting Britain by their use of these foreign troops.
Hessian soldiers were caught by surprise at the Battle of Trenton, when George Washington and his Continental Army crossed the Delaware River in the middle of the night. Following the war, a significant number of Hessian soldiers remained in North America, settling in both the United States and Canada. In "The Legend of Sleepy Hollow" by Washington Irving, the "headless horseman" is the ghost of a Hessian solider.