"That idea was the topic of a book a few years back (well, probably about ten years ago), did Buchanan cite anything? It wasn’t his idea." I have to give Buchanan his due, he writes like a serious historian, even though most historians, no doubt, do not consider him one. So the answer is "yes," everything is referenced to source material.
In this particular case, Buchanan's first point is not really controversial. Italy was allied with France and Britain during the First World War, and that alliance broke apart after the rise of Mussolini. The fault was primarily Mussolini's -- he was an arrogant SOB intent on conquest, and he offended the sensibilities of Britain's Antony Eden.
But Buchanan's more interesting point is that, at the time, Germany was still very weak, and a united front of Italy, France and Britain could well have put an early stopper on Hitler's territorial ambitions. So, by Britain's refusing to accommodate (or appease) Mussolini, they helped drive him into the much more dangerous arms of Hitler.
And, at the same time, by refusing to make nice with the disgusting dictator Mussolini, they were eventually forced to make very very nice with the far more dangerous dictator, Stalin!
So, Buchanan's theme is that Britain's interests would have been much better served if they had been more realistic, and less idealistic.
Well, I don't buy for one second that Eden was an idealist, nor do I think that Hitler was going to back down in any case -- it's as if Pitchfork Pat never heard of Von Ribbentrop's and Molotov's negotiations and the non-aggression pact between the USSR and the Third Reich. I suppose he discusses that too. Doesn't seem to understand it though. I guess he's never heard about how Eden brought down his party's government in Britain by his "idealism" in
the Suez Crisis -- but of course, Pat hates the Jews and Israel. Too bad such an intelligent guy is so [bleep]in' twisted.
But anyway...Italy wound up being enticed into the WWI alliance. The UK and France figured the A-H empire was at the breaking point (they said the same about Germany, and were dead wrong both times; by the time the US forces joined the fight in Europe, the BEF was wrecked; the larger but still mauled French army had not only learned from its mistakes, it also sent the appropriate personnel to help train the AEF, which went on to literally win the war for the Allies) so Italy was promised a generous slice of postwar Austria-Hungary if it would join the alliance and attack.
It turned out to be a stalemate for a long while (despite some claims made on behalf of Italy, the same kinds of claims made for the UK and France in that war) -- at least on enemy soil though -- then with a slight shift of resources, the Central Powers smashed Italian forces, forced a retreat and loss of some of Italy.
[the UK and France similarly enticed Romania, then screwed Romania when it turned quickly into a disaster during the German counterattack, which lasted about a month and reached the Black Sea]
The UK and France had to shift troops *into* Italy to prevent further loss of territory, then kinda shafted Italy in postwar arrangements. Given that, it's not too likely that anyone in Italy would have supported a second alliance with France and England. And Mussolini could see Hitler was serious, and wanted a piece of the pie Italy had been denied by its erstwhile allies.
The sense in which the war was unnecessary is really on the German side -- Hitler could probably have had it all, if he'd eaten up all the peripheral territories, then turned the Middle East to his own purposes, taken control of the Suez Canal, and taken over the oil supply, before he launched (or instead of launching) a two-front war against powerful European neighbors.
It was interesting to me that the German shifting of resources between fronts in WWII had been done in the same way (and for much the same reason) in WWI, and was even more successful in the earlier war.