I am very interested to discover the origins of my surname - GREINER.
I've always thought it was German (I've been to Germany and the name is in common use there, and it sounds German!)
However, recently I've discovered that my great-grandfather Oscar GREINER - born in the Alsace - considered himself to be a Frenchman. Obviously, today the Alsace is in France, but I think that at the time of Oscar's birth it would have been a part of Germany (1871-1918). I cannot find the information I need to confirm his date or place or birth and this is the advice I'm looking for here.
Oscar came to England certainly before 1915 ( I know this as he was working on-board the Lusitania when it was sunk by a German U-boat - he survived!

Can anyone advise me on where to look for birth records in France/ Germany/ German occupied France around the year 1900?
Thanks for your help
Lee