Wellington's army in the Peninsula included a non-British element, the King's German Legion and other regiments. In this it was not different from the armies of the day, the enlistment of foreigners being practised by all nations; and Great Britain was actually distinguished from other countries by prohibiting the custom in peace, though utilising foreigners extensively in war to make up for the weakness of the normal establishment.

Three types of foreign troops in British employment may be distinguished: subsidised allies, e.g. the Prussians in 1794, paid by Great Britain but not directly controlled; troops belonging to other countries (e.g. Hesse-Cassel) hired by Britain and under British control but not part of the Army; regiments which were raised for King George III.'s service and which formed part of the Army.

Of these the first were the least satisfactory, and the second were but little used after the Peace of Basle (1795) had neutralised North Germany. Most of the foreigners in our service belonged to the third class. These were obtained from various sources; at first French émigrés were available in large numbers, later on prisoners of war and deserters were enlisted. Some corps were raised directly in Switzerland (e.g. de Watteville's Regiment), and a few in Germany and Holland. The character of these corps varied greatly, some (e.g. the Queen's Germans, later known as the 97th, which did very well in Egypt in 1801) being really excellent corps.