Soldatenhandel
[5] Private mercenary groups played a significant military role in Medieval Europe, especially after the Kingdom of Germany was broken up.
[10] The Thirty Years' War ended with the Peace of Westphalia, which introduced the principle of Westphalian sovereignty in which each state has exclusive control over its own territory.
That was a significant step in the development of Soldatenhandel because smaller states could now raise their own armies and negotiate contracts with larger countries.
[2] The princes of the German states could establish mandatory service and offer cheaper prices than private mercenary contractors.
The Landgraviate of Hesse-Kassel, for example, leased soldiers to Denmark and Venice, supported William III of Orange in defending the Dutch Republic during his successful invasion of England in 1688, and it joined the Grand Alliance during the Nine Years' War.
[2] European legal experts such as Emer de Vattel argued that states could provide auxiliary forces to either side of a conflict without violating its neutrality.
[13] By the end of the 18th century, British Colonel William Fawcett wrote that it was no longer possible to recruit in Germany except with the permission of a state prince.
[15] For instance, Württemberg and Bavaria failed to secure treaties with Great Britain during the American Revolutionary War because they had not been financially able to keep regiments in a state of readiness.
[17] Although the soldier trade rarely generated a profit, the use of armed forces was a key factor in establishing diplomatic ties.
Prime Minister Sir Robert Walpole paid Hesse-Kassel an annual fee to keep its army ready to be called up.
In addition, as smaller states merged into the great powers of the late 19th century, the need for foreign auxiliary forces became less necessary.
[39] Recent scholarship suggests that Soldatenhandel was a necessary practice in early modern Europe for the small states providing military forces as well as for the larger kingdoms that were frequently drawn into wars.
