It wasn't wrong, just too early.

At the time international trade was still fairly minor, so although a war would be deeply unprofitable it'd still be possible. Today's economy looks quite different, with even basic consumer goods coming from overseas. If international trade were to suddenly cease, most major countries would be in serious trouble really quickly.

The most extreme example of this is the European Union. Its economies are so deeply interwoven that they act as a single entity. Separating them to the point that one of its members can independently support a war economy would take decades, so it does indeed make intra-European wars virtually impossible.

It doesn't make war impossible, just economically ruinous.

And yet it may be the best deterrent we have.

Make's war more unappealing to those that are rational, which is the best you can hope for because there is no sure fire way of dealing with the irrational.

Although I think wars do often have an irrational element, economic considerations aren’t the only ones that should influence rational decision making.

War is pretty hard when a decent portion of the thing you need to actually do war are made by the country you're at war with. Sure, you can start a war, but it'll be over when your local warehouses run out two weeks later.

It could be, but are there many historical examples of wars ending for this kind of reason? Typically, no country has its economy set up for wartime production during peacetime. But that can change quickly when there’s a will.

We survived the Cold War because the U.S. and the Soviet Union were able to rationally agree on not using nuclear weapons. I sure believe countries today can rationally agree on avoiding war for fear of the economic consequences.