Federalism has a long tradition in German history. The Holy Roman Empire comprised many petty states numbering more than 300 around 1796. The number of territories was greatly reduced during the Napoleonic Wars (1796–1814). After the Congress of Vienna (1815), 39 states formed the German Confederation. The Confederation was dissolved after the Austro-Prussian War and replaced by a North German Federation under Prussian hegemony; this war left Prussia dominant in Germany, and German nationalism would compel the remaining independent states to ally with Prussia in the Franco-Prussian War of 1870–71, and then to accede to the crowning of King Wilhelm of Prussia as German Emperor. The new German Empire included 25 states (three of them, Hanseatic cities) and the imperial territory of Alsace-Lorraine. The empire was dominated by Prussia, which controlled 65% of the territory and 62% of the population. After the territorial losses of the Treaty of Versailles, the remaining states continued as republics of a new German federation. These states were gradually de facto abolished and reduced to provinces under the Nazi regime via the Gleichschaltung process, as the states administratively were largely superseded by the Nazi Gau system.

The Holy Roman Empire comprised of how many petty states?