The Royal Prussian Army (1701–1919, German: Königlich Preußische Armee) served as the army of the Kingdom of Prussia. It became vital to the development of Prussia as a European political and military power and within Germany.
The Royal Prussian Army had its roots in the core mercenary forces of Brandenburg–Prussia during the long religious strife of the Thirty Years' War of 1618–1648. Elector Frederick William (1620–1688, reigned 1640–1688), developed it into a viable standing army, while King Frederick William I of Prussia (1688–1740, reigned 1713–1740), dramatically increased its size and improved its doctrines.