The book covers 400 years of the late Middle Ages across the whole of Europe, looking at how the boundaries of what can be considered Europe were expanding, and looking at the changing society of Europe over that time. The start of the period is just as the Viking etc raids were finishing when "Europe" is mostly the north-western part of modern Europe, and by the end (just before the Renaissance) it's much more recognisable. I'd not really realised before reading this book how much of eastern Europe was colonised so recently (relatively speaking) - even bits of Germany like Prussia were only settled by the Germans during this period.
I'm struggling to write much about the book - not through any fault of the book itself, it was well-written and interesting. More that I read it in chunks over several months, and then didn't even write it up very quickly after I finished it. So I've forgotten bits, and most of what I've forgotten is the sort of over-arching structure that would let me summarise more of the main points. Instead I've a head full of the neat little facts and ideas that it contained. It's a book I'll re-read sometime, I think on the second time through I'll know more of the incidental details so have more spare brain space to retain the over-arching ideas.