I've read recently that even if Germany let France keep Alsace-Lorraine after the Franco-Prussian War that France would still resent a united Germany because it would be far to great a geopolitical force in Europe. I've also read that a lasting Russo-German alliance was doomed due to German fears of being eventually dominated by Russia.
Regardless of how inevitable or not of Germany being surrounded by a hostile Franco-Russian Entente is, it got me wondering, if World War I or a similar war between at least Germany and Austria on one side and France and Russia on the other broke out in the early 20th century, how would France still having Alsace-Lorraine effect the strategies on both sides and how would it effect France's ability to wage war?