This map shows the German states at the time of the German unification in 1871. A catalyst in the process of unification was the Franco-Prussian war of 1870-1871, during which Prussia and its German allies occupied parts of France. The occupation lasted until 1874, to ensure reparations would be paid by the French. As a result of the war, Alsace-Lorraine was ceded by France to Germany. Many German states have issued stamps until, or even after – Bavaria and Württemberg – the German unification. Those that did not issue their own stamps were part of the postal system of other states or were serviced by the counts of Thurn & Taxis, that have operated a postal system in central Europe since the Middle Ages.