No, it really doesn't. It's pulp fiction fantasy.

I read it when it came out and I enjoyed it - as fiction. I like alternative histories - I've read many. I enjoyed the novel SS-GB 30 years ago far more, it was far more credible.

From memory... His whole argument is built on the assumption all Hitler wanted from Poland was the return of Danzig, and that all Germany wanted was peace and prosperity, but poor harmless Germany was surrounded by oppressive enemies. The same oppressors who spent 15 years appeasing whilst Germany occupied Rhineland, Austria and Sudetenland (Czechoslovakia) Well, there are so many ways to tear down the second point I barely know where to start.

So let's have a go at the first. He claims Hitler wanted Poland as an ally so clearly only wanted Danzig. So how better to gain an ally than invade them? So he starts trying to make a case that German diplomatic efforts were entirely honest and seeking to preserve peace. Further he dismisses the Polish politicians in short order (as some historians have done). It does rather raise the question of why then would Germany want an alliance.

Nonetheless they signed a non-aggression pact (note: not an alliance) in the mid 30s. Germany then sought to be given sovereignty of Danzig the surrounding region and roads leading to it (includig a half-built autobahn) in, I think 36 or 37. Poland declined, ultimately resulting in the 39 German ultimatum and invasion. Yup, definitely seeking an ally.

From there he builds on those unlikely assumptions and dives off into fantasy and antisemitism. Oh, and if Britain had accepted the Nazi's 1940 peace offer the Holocaust would not have happened at all. Even with all the antisemitism in Germany throughout the 30s and the propaganda and violence against them? Further he claims moral equivalence between Hitler and Churchill. Oh dear, really?

You could make a credible case of an unnecessary war, but it would resemble this book barely at all. There's a lot of arguments and ways you could approach that.

You might start with Churchill's (surprising given his history) actions as Chancellor in the 20s. The disastrous return to the Gold Standard, and by dramatically reducing defence budgets, especially naval, encouraged further German rearming and especially naval building. One of the few points I was able to agree with in the book was his criticism of Churchill's adoption of the Ten Year Rule. Though he makes it as a minor argument.

You might also point at the harsh terms of Versailles and the failure of the post-war alliance. It's worth noting Woodrow Wilson's 14 Points War Aims and instigation of the League of Nations. Not to forget the Americans never actually got as far as officially joining the League which significantly weakened the global standing of it. As far as reparations go it was Clemenceau who wanted harsh terms - mainly as so much of the war took place on French soil. With the obvious expenses that caused. Lloyd George argued firmly against excessive reparations. The United States Senate voted down the agreed 3 party post-war alliance with France and Britain. Churchill wanted an Anglo-French alliance in the absence of Americans to keep the continental peace but was unsuccessful. None were willing to occupy alone. Thus reoccupation of Rhineland, Sudetenland etc were rather easier than they should have been. The rest is factual history.

Forgive any mistakes. It'll all be on Wikipedia so I'm not going to link.