Original: During the Napoleonic Wars, the earl's art collection was inherited by the Wittelsbach family and moved to Munich, prompting the Prussian government-- who had annexed the Düsseldorf region after Napoleon had surrendered-- to change it into a Royal Arts Academy in Düsseldorf, in 1819.
Simplified: So the government of Prussia, who annexed the region of Düsseldorf after Napoleon surrendered, to open a new Royal Arts Academy in Düsseldorf.