When the leader of the Duchy of Prussia died without an heir in 1618, Brandenburg inherited his clay. He changed sides multiple times during the Thirty-Years War, eventually gaining independence from Poland-Lithuaniaball(his Prussian clay was still technically a vassal to them; isn't Feudalism fun?). During the second half of the 17th century, he honed his fighting skills until he was one of the best warriors in Europe. When Austria wanted help in the War of Spanish Succession, Prussia agreed to help him - on the condition that he could become the King in Prussia (as opposed to being the Duke of Prussia). Austria agreed, and in 1701 he became Kingdom of Prussiaball.