The years between the Franco-Prussian War and World War I were characterised by unusual political stability in Western and Central Europe. Although tensions between France and Germany persisted as a result of the French loss of Alsace-Lorraine to Germany in 1871, a series of diplomatic conferences managed to mediate disputes that threatened the general peace:, the Congress of Berlin in 1878, the Berlin Congo Conference in 1884, and the Algeciras Conference in 1906. Indeed, for many Europeans during the Belle Époque, transnational, class-based affiliations were as important as national identities, particularly among aristocrats. An upper-class gentleman could travel through much of Western Europe without a passport and even reside abroad with minimal bureaucratic regulation. World War I, mass transportation, the spread of literacy, and various citizenship concerns changed this.