Political map of Europe & the Mediterranean 3 May 1815 (Congress Poland): During the 1813 campaign against Napoleon (War of the Sixth Coalition), Prussia had agreed to the Russian rule over the Duchy of Warsaw in return for getting Saxony (Treaty of Kalisz (1813)). However, Austria and Britain opposed the deal, causing friction between the four powers. The situation was resolved in 1815 with the fourth partition of Poland between a Russian-dominated Polish Kingdom (Congress Poland), a Grand Duchy of Posen under Prussia, and a Free City of Cracow under the protection of its neighbors. Prussia was also granted much—but not all—of Saxony (Kingdom of Saxony)’s territory, as well as Swedish Pomerania.