From Hessians: Mercenaries, Rebels, and the War for British North America, by Brady J. Crytzer (Westholme, 2015), Kindle Loc. 326-348:
By January 1776 the British Empire had drafted agreements with five separate German princes including the regional powerhouse of Hesse-Cassel and its sister state of Hesse-Hanau. Along with these treaties there were also signed agreements with Brunswick-Wolfenbüttel, Anspach-Beyreuth, and the Principality of Waldeck. Later in 1777 the empire would ultimately settle terms with the relatively minor state of Anhalt-Zerbst, bringing their final treaty count to six separate German entities. Although these states would all furnish armies to sail to America and fight George Washington’s Continental Army, like all things in the Holy Roman Empire not all were equal in their contribution. The Landgrave of Hesse-Cassel Frederick II supplied the single largest armed force, 16,992 men, for a total sum of £2,959,800. The Duke of Brunswick provided 5,723 souls for £750,000, and Hesse-Hanau lent 2,422 men for £343,000. Margrave Karl Alexander of Anspach-Bayreuth sent 2,353 men, and signing over the least amount of soldiers were Prince Frederick of Waldeck at 1,225 and Prince Frederick Augustus of Anhalt-Zerbst at 1,160 for £109,120.
The treaties originally signed with the six individual German princes differed from each other in specifics, but all effectively offered the same general terms. The armies were “rented” for a term of six, seven, or eight years and the agreed-upon subsidy would go directly to the landgrave, duke, or margrave who ratified the treaty. The individual soldiers forced to serve in North America would receive none of those funds, but would be paid by the British Empire at roughly the same rate that they would pay their own regular soldiers. While the treaties were agreed upon in principle there were still small line items to be negotiated. One such point of contention was that some of the German princes demanded that London pay the soldiers’ salaries to the princes directly; British administrators balked at this assertion as they were almost certain that the dishonest German rulers would simply pocket the money for themselves. Another issue was the inevitable matter of wartime casualties, in which the British offered to reimburse the states for each man lost. Perhaps the most startling development, though, came from the inclusion of a contracted casualty reimbursement; for every man killed or wounded their prince would be additionally compensated in turn. The German soldier traveled to the New World knowing that he was, quite literally, worth more dead than alive.
By the winter of 1776 the British Empire had contracted nearly eighteen thousand German soldiers to travel to North America and suppress the growing revolt that was stirring in the Atlantic colonies. Of those men over half were provided by Hesse-Cassel, therefore the term “Hessian” would be generically applied to all German auxiliaries employed in the New World. For the unlucky soldier commanded by his feudal lord to travel across the sea and battle the American rebels there was little hope; they were doomed to fight a rebellion for which they stood to gain nothing.