One of the best books I've ever read. I still keep a copy on my phone to re-read when I have 10 minutes to wait somewhere.
Up through my teenage years, I was a World War II buff. Since then I haven't covered too much of it; I don't feel there's too much for me to learn so my time is better spent elsewhere.
But, a while back, I was wondering how Germany beat France so quickly. I did know a lot about this, but more from a strategic perspective. I asked for recommendations on Quora, and this one got multiple likes.
It's 2019, and I recommend you read this with something like Google Maps available on a big screen computer. It doesn't dominate the book, but all over there's a sense that the generals of both countries were thinking in terms of the road net, so a road map will help you out. Also, the reputation is that the German attack through the Ardennes was somehow heroic because the country was so rough. But you read it and you realize they didn't do the thing cross-country: they followed the few roads that went through the Ardennes (and the Allies made a huge blunder by not effectively bombing the huge lines of traffic). They didn't need a thicker road net, they needed just enough of a road net.
You also get a very strong sense throughout of the huge level of denial on the part of the French. They thought they were doing OK for much of the battle. But you learn that a lot of them seemed to be off in a fantasy world, or unable to process reports effectively. In fact, probably the first quarter of the book is devoted to the goofed up politics of France in the 1930's, and how this contributed to the whole military system not functioning very well.
And the Germans were much more pessimistic. Especially the top generals back at headquarters. They were very worried about the whole thing, going back to the original planning in 1939. They didn't feel Germany had re-armed enough to take on France. Only Hitler, and the generals on the front, were confident that things were going their way.
Parts of the plan worked well. In 1871 the Germans had attacked through the center. In 1914 they attacked on the French left. This was more successful. And the French, knowing everyone was more mechanized in 1940, anticipate the Germans hitting the French left where the road net was thicker. So, when the attack started, the French and British advanced on their left, but the Germans came through the center (and ultimately cut off the Allied left flank, leading to Dunkirk).
And the French put some of their weakest units in their center, presuming the Germans would never bring mechanized stuff through the center. Even worse, they had the border between two armies in the center. And the Germans came west on 3 different roads and hit 3 different river crossings at about the same time, one of which was near the border between the two weak French armies.
Even so, it was a near thing. One hears stories that the French fought effectively at the small group level, and this is mostly correct. And the Germans concentrated their armor, and this is correct (a bigger problem was that when the French brought up their armor, they couldn't hit the Germans, who tended to move on quickly).
One also hears a lot about the usage of air support in German blitzkriegs. This was not new to me, but this book clarified a lot. The French had always taken huge pride in their artillery. And the soldiers in the field felt they were protected by the artillery barrage coming from behind. One of the big military restrictions on Germany was on artillery (because it was used so much in World War I). And it's expensive, and easily monitored, so the Germans built planes instead. So when the battle was joined, the Germans sent their planes after the French artillery batteries a few miles behind the lines, and effectively shut them down. When those long barrels stopped firing, the infantry up front started to melt away. This was a big problem where the two French armies bordered, because the Germans opened a whole that neither army felt responsible to fill.
Then it was a free for all. And the Germans commanders on the ground surprised everyone on both sides by ... driving. And really not very far: after all, these are tanks and cars in 1940, on mostly unpaved roads. Even so, the Germans broke through on those 3 crossings, and soon their armor was following the roads every which behind the French lines. The French or British would counterattack in one area, and then here news that it didn't matter because the Germans were already in half-a-dozen towns several miles to the west.
In retrospect, it's fairly obvious that this could have been defended with more defense in depth, and more air power. But there was essentially no defense in depth at any little village with a crossroads. By then the French had lost the ability to command smaller units to get out front of the Germans and dig in. So the Germans just kept driving. And the air power of both the British and French was stunningly disorganized. Yes, their planes weren't great, but they couldn't get them in the air with any alacrity. All they had to do was start bombing the traffic lines to turn them into traffic jams, and they managed basically zero of this.
I also found the shuttle diplomacy of Churchill towards the end of the book to be fascinating. It was a brand new thing for a leader of one country to fly over to their allies to talk face-to-face. Churchill did this more than once. And what he found was that the French had trouble establishing who was in charge, who was responsible, who to send order to, and so on.
The book winds down fairly abruptly, and does not cover the fall of France in any depth. After a week or two, France was done for, even though the Germans had not advanced yet as far as they had in World War I.