They should know better than that by now, but then Europe was never smart to begin with. They never learned the lessons of two World Wars.
Technically what we call world war 1 and 2 were the same war with a 20 year pause in between. If the entente in 1918 had invaded imperial Germany in 1919 then no stan in the back and no nazis.
And there were two world wars before 1914: the war of Spanish succession (the French and indian war was the north american chunk of it and there were wars in Asia) and the Napoleonic wars were fought in 3 continents