In 1415 a member of the Hohenzollern family had been given sovereignty over Brandenburg, of which Berlin was the capital. Prussia, a separate duchy in Poland, was in 1618 joined with Brandenburg by inheritance. At the Peace of Westphalia, Frederick William of Brandenburg called the Great Elector, acquired some of the area between Brandenburg and Prussia. He later gained Prussia's freedom from Poland and confirmed his title to two small states in western Germany. From this patchwork of possessions came the future Germany. The Great Elector left Brandenburg economically and militarily strong.

Meanwhile, in 1686, several German states joined the League of Augsburg, which later became the Grand Alliance. The Alliance opposed the expansionist policies of the French king, Louis XIV, and fought the War of the Grand Alliance (1689-97) to stop him. The war ended in a stalemate, but they did thwart Louis' expansion into Germany.

Frederick, the Great Elector's son, was an ambitious ruler. He assisted the Holy Roman Emperor in wars against France and the Turks. In return, the Hohenzollern domain was made the kingdom of Prussia by the Holy Roman Emperor in 1701. Frederick assumed the crown as Frederick I. His son Frederick William I (ruled 1713-40) defeated the Swedes in the Northern War (1700-20). As a result, Prussia gained more territory on the Baltic.