King in Prussia
In return for an alliance against France in the War of the Spanish Succession, the Great Elector's son, Frederick III, was allowed to elevate Prussia to a kingdom in the Crown Treaty of 16 November 1700. Frederick crowned himself "King in Prussia" as Frederick I on 18 January 1701. Legally, no kingdoms could exist in the Holy Roman Empire except for Bohemia. However, Frederick took the line that since Prussia had never been part of the empire and the Hohenzollerns were fully sovereign over it, he could elevate Prussia to a kingdom.