Treaty of Frankfurt (1871) in the context of "German unification"

Haut-Rhin (French pronunciation: [oʁɛ̃] ) is a department in the Grand Est region, France, bordering both Germany and Switzerland. It is named after the river Rhine. Its name means Upper Rhine. Haut-Rhin is the smaller and less populated of the two departments of the former administrative Alsace region, the other being Bas-Rhin (Lower Rhine), especially after the 1871 cession of the southern territory known since 1922 as the Territoire de Belfort, although it is still rather densely populated compared to the rest of metropolitan France. It had a population of 767,083 in 2021.

On 1 January 2021, the départemental collectivities of Bas-Rhin and Haut-Rhin were merged into the European Collectivity of Alsace.

The Unification of Germany (German: Deutsche Einigung, pronounced [ˈdɔʏtʃə ˈʔaɪnɪɡʊŋ] ) was a process of building the first nation-state for Germans with federal features based on the concept of Lesser Germany (one without the Habsburgs' multi-ethnic Austria or its German-speaking part). After the deletion of the German Confederation due to the Austro-Prussian War, it commenced on 18 August 1866 with the adoption of the North German Confederation Treaty establishing the North German Confederation, initially a military alliance de facto dominated by the Kingdom of Prussia which was subsequently deepened through adoption of the North German Constitution.

The process symbolically concluded when most of the south German states joined the North German Confederation with the ceremonial proclamation of the German Empire (German Reich) having 25 member states and led by the Kingdom of Prussia of Hohenzollerns on 18 January 1871; the event was typically celebrated as the date of the German Empire's foundation, although the legally meaningful events relevant to the completion of unification occurred on 1 January 1871 (accession of South German states and constitutional adoption of the name "German Empire"), 4 May 1871 (entry into force of the permanent Constitution of the German Empire) and 10 May 1871 (Treaty of Frankfurt and recognition of the Empire by the French Third Republic).

Alsace–Lorraine (German: Elsaß–Lothringen), officially the Imperial Territory of Alsace–Lorraine (German: Reichsland Elsaß–Lothringen), was a territory of the German Empire which is now part of France. It was established in 1871 by the German Empire after it had occupied the region during the Franco-Prussian War. The region was officially ceded to the German Empire in the Treaty of Frankfurt. French resentment about the loss of the territory was one of the contributing factors to World War I. Alsace–Lorraine was annexed in practice by France at the war's end following Germany's defeat in 1918, but only formally ceded back in 1920 as part of the Treaty of Versailles.

Geographically, Alsace–Lorraine encompassed most of Alsace and the Moselle department of Lorraine; the Alsatian part lay in the Rhine Valley on the west bank of the Rhine River, east of the Vosges Mountains, while the section initially in Lorraine was in the upper Moselle valley to the north of the Vosges. Politically, it was the only subdivision of the German Empire considered an "Imperial Territory"; as such, it was under the direct administration of the Imperial German state, rather than a quasi-sovereign constituent of the federal Empire. It was granted a legislature and limited internal autonomy in 1911.