Treaties of Tilsit
New Silesia had its capital at Siewierz. However, it was originally to be governed by the Silesian capital Breslau (Wrocław) and later largely administered by South Prussia. After the defeat of Prussia in the War of the Fourth Coalition in 1806, the province was dissolved and the territory was made part of the Napoleonic Duchy of Warsaw in the Treaties of Tilsit of 1807.