The Long Shadow is about the legacies of the First World War. The first half of the book deals with the effects it had in a number of different eras going forward. Politics, literature, that sort of thing. Most of this is focused on the time prior to and during the Second World War. The second half deals with how differently it was viewed after WW2, how that experience shaped how people interpreted the first one.
This is not exactly what I expected when I started reading it. I also wasn't expecting it to be so heavily focused on Britain, because that's where I'd say Reynolds focuses a solid two-thirds of the book. He will usually, in any given section, briefly discuss Germany, France, the United States, and maybe the Soviet Union or Japan as seems relevant, but it mostly keeps coming back to England.
Mostly because Reynolds finds their reactions to be so different. Their government doesn't collapse into a totalitarian one after the war, and expanding the electorate doesn't bring about any sort of societal collapse. There's also the fact that for Britain, the threat to their country in WWI was remote for the most part. They had generally framed their involvement as reacting to "Hunnish" aggression against poor Belgium. This made it harder to justify the loss of life, especially when 20 years later, it didn't seem to have accomplished anything, because here come the Germans again, bigger and more dangerous than ever.
If you studied American literature in school, you probably were taught about the "lost generation" of writers in the 1920s, who struggled to find meaning after the experiences with the First World War, and struggled to find meaning in that war. The way it comes off here, there was some of that in England, but it didn't actually achieve a mass consciousness until the 1960s, when it was contrasted so unfavorably with their "finest hour".
All of this can be interesting, but it can also be immensely tedious. I don't even enjoy reading poetry, you can imagine how little interest I had in reading about poetry. And, again, I expected a somewhat broader focus. I expected more about how the decisions made while drafting the Versailles treaty had long-reaching effects in the new countries created out of it, or in the places that got short-changed. Like China, where Japan was allowed to maintain control of the territory they took from Germany. Or the Middle East, where the British and French formed a bunch of "mandates" that they'd run to various degrees until they decided the people there were capable of governing themselves. Or anything much at all about Africa. I figured just for how it shook up the various imperial powers there would be some impact, either in giving independence groups new hope, or resulting in a crackdown by the authorities (which produces its own reaction), or something. And Reynolds does discuss India, a bit, but again, mostly in the context of England.
It was a book with just enough interesting bits to keep me plodding through all the stuff I either already knew or didn't care for.
'This peculiar British preoccupation with the Great War via poetry rather than history became dominant during the 1960s. It reinforced another contemporary trend, emphasizing the experiences of individual soldiers rather than the big-picture issues of strategy and diplomacy, finance and production. This trend was evident elsewhere in Europe in the 1960s and 1970s, but as we shall see in the next chapter, once again the British pattern was unusual.'