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.

King Frederick the Great (1712–1786, reigned 1740–1786), a formidable battle commander, led the disciplined Prussian troops to victory during the 18th century Silesian Wars and greatly increased the prestige and military reputation throughout Europe and among the hodge-podge array of various German states kingdoms, duchies, principalities and free cities of the leadership in the East of the rising Kingdom of Prussia.

[1] The elector's confidant Johann von Norprath recruited forces in the Duchy of Cleves and organized an army of 3,000 Dutch and German soldiers in the Rhineland by 1646.

[2] Frederick William sought assistance from France, the traditional rival of Habsburg Austria, and began receiving French subsidies.

[3] The growth of his army allowed Frederick William to achieve considerable territorial acquisitions in the 1648 Treaty of Westphalia, despite Brandenburg's relative lack of success during the war.

The provincial estates desired a reduction in the army's size during peacetime, but the elector avoided their demands through political concessions, evasion and economy.

[9] Hohenzollern success enabled Frederick William to assume full sovereignty over the Duchy of Prussia in the 1657 Treaty of Wehlau, by which Brandenburg-Prussia allied itself with the Polish–Lithuanian Commonwealth.

[7] Its success in battle against Sweden and Poland increased Brandenburg-Prussia's prestige, while also allowing the Great Elector to pursue absolutist policies against estates and towns.

[20] The General War Commissary, responsible for the army and revenue, was removed from interference by the estates and placed strictly under the control of officials appointed by the king.

[22] Until 1730 the common soldiers consisted largely of serfs recruited or impressed from Brandenburg, Pomerania and East Prussia, leading many to flee to neighboring countries.

Every youth was required to serve as a soldier in these recruitment districts for three months each year; this met agrarian needs and added troops to bolster the regular ranks.

[24] The General Directory which developed during Frederick William I's reign continued the absolutist tendencies of his grandfather and collected the increased taxes necessary for the expanded military.

For his great services at Hohenfriedberg Hans Karl von Winterfeldt, a good friend of King Frederick, rose to prominence.

Frederick achieved one of his greatest victories, however, at Rossbach, where the Prussian cavalry of Friedrich Wilhelm von Seydlitz smashed a larger Franco-Imperial army with minimal casualties, despite being outnumbered two to one.

Scharnhorst promoted the integration of the infantry, cavalry, artillery, and engineers (sappers) through combined arms, as opposed to their previous independent states.

When the cautious king refused to support a new Prussian war, however, Schill led his hussar regiment against the occupying French, expecting to provoke a national uprising.

With Prussia's joining of the Sixth Coalition out of his hands, Frederick William III quickly began to mobilize the army, and the East Prussian Landwehr was duplicated in the rest of the country.

In the same year Boyen and Grolman drafted a law for universal conscription, by which men would successively serve in the standing army, the Landwehr and the local Landsturm until the age of 39.

Frederick William III reduced the militia's size and placed it under the control of the regular army in 1819, leading to the resignations of Boyen and Grolman and the ending of the reform movement.

King Frederick William IV (1840–61) initially appeared to be a liberal ruler, but he was opposed to issuing the written constitution called for by reformers.

General Friedrich Graf von Wrangel led the reconquest of Berlin, which was supported by a middle class weary of a people's revolution.

The Finance Minister, Patow, abruptly withdrew the bill on 5 May and instead simply requested a provisional budgetary increase of 9 million thalers, which was granted.

The liberal and middle-class Landwehr was thus subordinated in favor of the regular army, which was composed mostly of peasantry loyal to the Hohenzollern monarchy and conservative Junkers.

[67] In 1869, he issued a handbook for warfare on the operational level, Instructions for Large Unit Commanders, writing, "The modern conduct of war is marked by the striving for a great and rapid decision".

[68] Moltke was a strong proponent of war game training for officers[68] and introduced the breech-loading needle gun to troops, which allowed them to fire significantly faster than their adversaries.

The system of moving units separately and concentrating as an army before a battle resulted in more efficient supply and lower vulnerability to modern firepower.

A major consequence of this innovation was the commander's loss of overall control of his forces due to his available means of communication which, at that time, were visual (line-of-sight) or couriers, either mounted or on foot.

The traditional concept of the elimination of uncertainty by means of "total obedience" was now obsolete and operational initiative, direction and control had to be assigned to a point further down the chain of command.

By the end of the 19th century, most Prussian officers could be divided into two groups: those who argued for boldness and self-sacrifice, and those who advocated technology and maneuver in order to minimize casualties.

The Hohenzollern state often had fewer resources and manpower than its rivals, and thus the Prussians focused on quickly achieving decisive battlefield victories to avoid wars of attrition/sieges.