Thanks for that. I hadn't realised that Eupen was German speaking.
When we did the Salzburg trip we stopped in the Saarland on the way back. (Zweibruecken I think but it was a while ago). A bit of Googling afterwards was interesting - the French didn't fully let go of the Saarland until the 1980s - presumably when all the coal was gone.
In Our Time today did the Siege of Paris. I've always had a view that WW2 was the 3rd Franco-Prussian war.