Prussia in its modern meaning came into existence only in 1701, when the elector of Brandenburg assumed the title "king in Prussia." Before then Prussia meant only the flat, sandy region later known as East Prussia (excluding the bishopric of Ermeland), separated from Brandenburg by a part of Poland (later known as West Prussia) and bordering on the Baltic Sea. The original inhabitants, the Borussi (or Prussians), were of Baltic stock. They were conquered and largely exterminated by the Teutonic Knights in the 13th cent. The Knights effected the Germanization of Prussia.

Through the secularization (1525) of the domain of the Teutonic Order by the grand master Albert of Brandenburg, the domain became a hereditary duchy under Polish suzerainty, ruled by a branch of the Hohenzollern dynasty of Brandenburg. In 1618 the duchy of Prussia passed through inheritance to the elector of Brandenburg, and in 1660, by the treaty of Oliva, full independence from Polish suzerainty was confirmed to Frederick William, the Great Elector. In the course of the 17th cent. the electors of Brandenburg directed themselves westward, acquiring the duchy of Cleves, together with the counties of Mark and Ravensberg (1614) and the bishoprics of Minden, Magdeburg, and Halberstadt (1648). In the east, Brandenburg gained (1648) Farther (i.e., eastern) Pomerania, which connected it with the Baltic Sea but not with Prussia.

The electorate with its dependencies had become a major German state by the end of the 17th cent., a position that it owed largely to the secularization of church lands during the Reformation (the major part of its new acquisitions had been ecclesiastic territory) and to its successful diplomacy at the Peace of Westphalia (1648). In 1701, Elector Frederick III had himself crowned "king in Prussia" at Königsberg (Kaliningrad) and styled himself King Frederick I. He remained a prince of the Holy Roman Empire by virtue of his rank as margrave and elector of Brandenburg and his holdings within the empire, but not as king of Prussia, which lay outside the imperial boundaries. This technicality gave the kings of Prussia a measure of independence from the emperor not possessed by the other princes of the empire.

As a result of the Northern War, Prussia gained (1720) the eastern part of Swedish Pomerania (including Stettin). In the following 20 years, however, King Frederick William I, the true creator of the Prussian state, avoided military ventures and used diplomacy in order to create a unified state. He fully developed the features that had distinguished Prussia since the time of the Great Elector. The army, necessary to defend Prussia's scattered lands, was also the chief force in unifying and shaping the state. In order to build a strong army in their relatively poor country, Prussia's rulers developed a government-controlled economy and an obedient central bureaucracy (the Generaldirektorium). The landed aristocrats, the Junkers, were brought into military and state service and in turn were left free to enserf their peasants.

Frederick William's successor, Frederick II, or Frederick the Great (reigned 1740-86), used the efficient military instrument bequeathed him by his father to enter upon a period of conquest. On a slim pretext (see Silesia) and without a declaration of war, he invaded (1740) Austrian territory, thus gaining the initiative in the War of the Austrian Succession (1740-48). Acting with utter disregard for its allies, Prussia got out of the war in 1742 by the Treaty of Berlin, reentered it in 1744, and quit again in 1745 at the Treaty of Dresden. In both treaties Maria Theresa of Austria was forced to cede nearly all of Silesia to Prussia. Although it gained no additional territory in the Seven Years War (1756-63), Prussia emerged from the war as the chief military power of the Continent. By the partition of Poland of 1772 (see Poland, partitions of) Prussia gained Pomerelia (except Danzig) and Ermeland. Pomerelia was organized into the province of West Prussia, and the original Prussia became known as East Prussia.

Frederick was succeeded (1786) by Frederick William II, who further added to Prussia by the partitions of Poland of 1793 and 1795. However, under his rule and that of his successor, Frederick William III (1797-1840), Prussia underwent a period of eclipse as a result of the French Revolutionary Wars and the wars of Napoleon I. Defeated by the French, Prussia withdrew from the antirevolutionary coalition in the Treaty of Basel (1795) and remained neutral until 1806. Its armies were crushed by Napoleon in the twin battles of Jena and Auerstedt, and in 1807 Prussia had to accept the harsh Treaty of Tilsit, by which it lost all lands W of the Elbe and most of its share of Poland and became a virtual dependency of France.

Prussia was fortunate to possess, at this low ebb in its history, such able and energetic reformers as Karl vom und zum Stein, Karl August von Hardenberg, and Wilhelm von Humboldt. These men helped transform Prussia into a progressive state by abolishing serfdom and nobiliary privileges, introducing agrarian and other social and economic reforms, and laying the groundwork for an exemplary system of universal education. Gerhard von Scharnhorst and August, Graf von Gneisenau at the same time put the Prussian army on a modern basis.

Prussia was forced to send auxiliary troops for Napoleon's 1812 campaign in Russia, but late in the year Yorck von Wartenburg concluded a separate truce with Russia, and in 1813 Prussia joined the coalition against France. Field Marshal Blücher played a major role in defeating Napoleon at Leipzig (1813) and at Waterloo (1815). At the Congress of Vienna, Prussia gained, in addition to its recovered territories, the entire Rhine prov. and Westphalia, the northern half of Saxony, the remainder of Swedish Pomerania, and a large part of W Poland, including Danzig (Gdańsk), Poznań, and Gniezno. However, Prussia disappointed the hopes of German liberals by following the lead of the Austrian chancellor, Metternich, in the Holy Alliance.

A constitution promised in 1811 failed to materialize under the increasingly reactionary government of Frederick William III, and the half-hearted constitutional schemes of Frederick William IV were impracticable. By 1834 Prussia had, however, taken the lead in the economic unification of Germany (see Zollverein), which was a prerequisite to political union. The March Revolution of 1848 was put down by force, and in 1849 Frederick William IV refused the imperial crown of Germany offered by the Frankfurt Parliament. His scheme for a German Union under Prussian leadership and excluding Austria was punctured in the Convention of Olomouc (1850), and Prussia returned to the restored German Confederation.

In 1861, William I (regent since 1858) became king, and in 1862 he appointed as premier Otto von Bismarck, who directed the destiny of Prussia and (after 1871) of Germany until 1890. Bismarck effected the elimination of Austria from German affairs and the union of Germany under Prussian hegemony by means of three deliberately planned wars. The first war (1864) was fought in alliance with Austria against Denmark over Schleswig-Holstein. Its settlement furnished a pretext for the Austro-Prussian War of 1866, in which Prussia quickly and thoroughly defeated Austria and its allies and gained additional territory by the annexation of Hanover, Electoral Hesse, Nassau, Schleswig-Holstein, and the free city of Frankfurt am Main. The German Confederation was dissolved, and the Prussian-led North German Confederation took its place. Finally, in the Franco-Prussian War (1870-71), the North German Confederation overwhelmed France, and in 1871 William I of Prussia was proclaimed emperor of Germany.

In its main features the subsequent history of Prussia was that of Germany. However, Bismarck's Kulturkampf against the Roman Catholic Church was largely confined to the kingdom of Prussia, which, like the other German states, continued as an individual member of the empire.

The Prussian constitution adopted in 1850 and amended in the following years was far less liberal than the federal constitution of the empire. The government was not responsible to the Prussian Landtag (lower chamber), whose powers were small and whose members were elected by a suffrage system based on tax-paying ability. The house of lords was largely controlled by the conservative Junkers, who held immense tracts of generally poor land E of the Elbe (particularly in East Prussia). Endowed with little money and much pride, they had continued to form the officer corps of the army. The rising industrialists, notably the great Rhenish and Westphalian mine owners and steel magnates, although their interests were often opposed to those of the Junkers, exerted an equally reactionary influence on politics. The Prussian constitution was liberalized after Prussia became a republic in 1918, and the Junkers lost many of their estates through the cession of Prussian territory to Poland. However, both the Junkers and the Rhenish industrialists continued to exert much power behind the scenes, and when Franz von Papen became (1932) German chancellor and commissioner for Prussia, they came into their own. In July, 1932, Papen suspended the Prussian parliament and ousted the Social Democrat Otto Braun, who had been premier of Prussia (with brief interruptions) from 1920.

Early in 1933, Adolf Hitler seized power and made Hermann Goering premier of Prussia; Hitler's rise had been aided by the Rhenish industrialists. By a decree of Hitler issued in Jan., 1934, the German states ceased to exist as political units, and it was no longer possible to differentiate clearly between Prussia and the rest of Germany. After World War II, in 1947, Prussia was officially dissolved by the Allied Control Council, which characterized the state as "a bearer of militarism and reaction in Germany." The former state was divided among the former West and East Germanies, Poland, and the USSR's Russian Republic (now Russia).