British military officials employed the common European practice of hiring mercenary soldiers for the war in America. Given that Germany was not unified at this time, most principalities maintained their own military forces, Hesse-Cassel among them. Even though mercenaries came to America from other German states, they were known, then and now, as Hessians.
It is estimated that nearly 30,000 Germans served with the British in America. The attraction of free land for deserters and the vigorous German population already in America led thousands of these mercenaries to switch allegiance and stay in America.
Hessians who remained in the British employ were hated and feared by the Americans, and the fact that George III had chosen to employ foreign mercenaries stirred up much anger among the colonists.