Everybody just assumes that the Allies were bound to win, but if you look at the early period you can see that it was far from inevitable. Overy does a fantastic job of analysing WHY.
One of the issues he addresses is our bombing campaign which so many people nowadays love to denigrate. It was actually crucial to our winning.
The Nazis in charge had every reason to downplay the figures of just what it was costing, but even they admitted to something like 40% of industrial production lost or diverted to air defence. So much air defence required against bombers that they lacked air superiority in crucial battles like Kursk. So much ammunition converted to anti-aircraft production that they lacked supplies on the front line and even lacked fertiliser for producing food.
At the end of the day you can only fight if you have the weapons and ammunition to do it with, so it becomes a battle between respective economies. On the Axis side only Germany really ramped up production. Russia did an outstanding job, with her people caught between a vicious onslaught by National Socialist who called them sub-humans and their own International Socialist rulers who barely treated them much better.
And nobody could believe what the US economy proved capable of - the most accurate estimates were made by the British but even these were way off.
It might sound dry but it doesn't read that way - highly recommended.