Anna, daughter of Duke Albrecht Friedrich of Prussia (r.1568-1618), married Elector Johann Sigismund of Brandenburg, who succeeded to the Province on his father-in-law's death in 1618. From this time, Ducal Prussia became a possession of the Electors of Brandenburg.
During the reign of Georg Wilhelm (1619-1640), the Hohenzollern lands were repeatedly marched across by various armies in the Thirty Years War, spending much of the war occupied by Sweden. Taking advantage of the difficult position of Poland with Sweden in the Northern war, and their friendly position with Russia during a series of Russo-Polish wars, "The Great Elector" Friedrich Wilhelm (1640-1688) obtained a discharge of his vassal obligations and after the Tatar invasion of Poland in 1656-57, was finally given independent control of Prussia in 1660. In 1701 his son, Friedrich III, proclaimed himself Friedrich I, King in Prussia.
The Kingdom of Prussia existed from 1701 through 1918 under the rule of Brandenburg which became the leading kingdom of the German Empire, comprising in its last form almost two-thirds of the area of the Empire. In 1688, Frederick William I, the "Great Elector", died and his possessions passed to his son Frederick III (1688-1701) who became Frederick I of Prussia (1701-1713).
With the exception of Prussia proper, all of Brandenburg's lands were a part of the Holy Roman Empire, by this time under the all but hereditary nominal rule of the House of Habsburg. Since there was only one King of the Germans within the Empire, Frederick gained the assent of the Emperor Leopold I (in return for alliance against France) to his adoption (January 1701) of the title of "King in Prussia", based on his non-Imperial territories, and the title came into general acceptance with the Treaty of Utrecht (1713). Though Brandenburg was far richer and more important than Prussia proper, it was subsumed into The Kingdom of Prussia in a change understood by all to be a shell game with titles. Thus the new nation is also commonly called Brandenburg-Prussia.
During this time the trends set in motion by the Great Elector reached their culmination, as the Junkers - the landed aristocracy - were welded to the army which had gained so much influence in the previous fifty years.
To the surprise of many, Austria managed to renew the war successfully, and in 1744 Frederick invaded again to forestall reprisals and to claim, this time, the province of Bohemia. This time he failed, but French pressure on Austria's ally Britain led to a series of treaties and compromises (culminating in the 1748 Treaty of Aix-la-Chapelle that restored peace and left Brandenburg-Prussia still in possession of Silesia.
Humiliated by the cession of Silesia, Austria worked to secure an alliance with France and Russia, while Brandenburg-Prussia drifted into the United Kingdom's camp (the "Diplomatic Revolution". When Frederick pre-emptively invaded Saxony and Bohemia over the course of a few months in 1756-1757, a general conflict broke out: the Seven Years' War.
In 1772 King Friedrich II annexed the Polish province of Royal Prussia, without the Gdansk territory, from the Kingdom of Poland, and united it with Ducal Prussia (it now taking the name East Prussia). In 1793, King Friedrich Wilhelm II annexed the areas around Gdansk and Torun. In 1793 and 1795, larger areas of Poland were added, which were organized into the Provinces of South Prussia and New East Prussia. Like many countries in Eastern Europe at that time, the old Polish Kingdom was inhabited by many ethnic groups, and it is important not to confuse political loyalties with ethnic identities. Many loyal Polish subjects were not ethnically Polish. Western Prussia, including Gdansk, had had a ethnic German majority for centuries, while a sizable German minority lived in the Torun area. Other important ethnic groups, besides Poles, were Jews. Some locals even descended from hardy Scotsmen, who had fled to Gdansk in the 16th century, and founded the suburb of New Scotland.
The Kingdom of Prussia at this time was not part of Germany. K�nigsberg was the capital and coronation city of the Prussian kings. In 1806 Napoleon Bonaparte conquered Europe and abolished the German empire and the title of Kaiser for Germany (capital: Wien [Vienna]). The Kaiser in Wien became Kaiser of Austria with no power in the rest of Germany. The titles of Kurf�rst (elector) became meaningless and was abolished and changed to Kings of Bohemia, (Brandenburg-)Prussia, Saxony, Bavaria, Wuerttemberg, and Hannover by Napoleon's grace. The archbishops and Catholic church had lost all their secular power in 1803.
After Napoleon's final defeat in 1815 The Kingdom of Prussia became known as "Die Vereinigten Preussischen Staaten" (The United Prussian States) which now also included provinces like Silesia, Brandenburg, Pomerania and areas as far west as the Rhine province. Brandenburg's Berlin now became the Brandenburg-Prussian capital. Until 1806 the Hohenzollern sovereign had had many titles and hats from Head of the Evangelic Church to King, Elector, Grandduke, Duke for the various regions and realms under his rule. After 1806 he simply was King of Prussia. Terms like German government or German army have no meaning for this time period until 1871.
In 1918, Prussia-Brandenburg ceased to exist as a state as it was absorbed into the Weimar Republic.