Prussia (and subsequently, the German Empire) stole Alsace from France (under Napoleon III) after the German victory in the Franco-Prussian War
Wrong again Pilsner!
In prehistoric times, Alsace was inhabited by nomadic hunters, but by 1500 BC, Celts began to settle in Alsace, clearing and cultivating the land. By 58 BC, the Romans had invaded and established Alsace as a center of viticulture. To protect this highly valued industry, the Romans built fortifications and military camps that evolved into various communities which have been inhabited continuously to the present day. While part of the Roman Empire, Alsace was part of Germania Superior. The Kingdom of Lotharingia was short-lived, however; the region that was to become Alsace fell to the Holy Roman Empire as part of the Duchy of Swabia in the Treaty of Meersen in 870...
The Elsaß also never got ethnically cleaned and is now
inhabited by people with both french and german roots - even if the whole of France is very germanic anyhow...they even got their name from a german tribes confederation, the Franks.
Alsace is so not like Silesia! The french are not Poles!!! :)
Germans and French share one of the most important Europeans ever: Charlemagne aka Karl der Große:
He laid the foundations for what should later become France and Germany...