Giles MacDonogh is the author of several books on European history, including “After the Reich.” He is currently working on “Hitler’s Germany: A Social History of the Third Reich.”

It all looked like a pretty good idea in 1951: A world war had come to an end only six years earlier and a cold one followed in its wake. Old enemies were about to become new friends.

The first step was barter. Instead of milking the defeated nation’s resources — the ancient way of war — they could be shared: You have coal, we have steel; we’ll swap. This fair trade was at the heart of the Treaty of Paris, the beginning of the European Coal and Steel Community, the seed that became the mighty European Union....

It has now been 68 years since the end of World War II, and in Western and Central Europe at least, peace has reigned for the longest period in modern history — trouncing the calm that ran from Waterloo to the Crimean War by nearly two decades.

It would be a pity to forget a century of good, hard work or the 60 years we have spent burying our differences and throw it all away at the toss of a coin.