The economics of depression-era America was a sad, sorry, tedious mess. The opportunist speculators were basically running the show, the general public was being oblivious to the disaster mounting: every boom has to end, it either will dissipate or topple over in a huge loss, and the bigger it gets the worse the problem. Galbraith had a very classical skepticism toward the whole situation, one that defined a nation in the worst possible conditions. Without the great depression, the stock market would be a quite superficial establishment; it would have had no checks and balances.
Galbraith chose to write this book because he felt that the actual truth behind the crash needed to be put in a form that the public could understand, and that the public would recognize. The real causes of the stock market collapse were pretty much veiled to the whole country. That is why Galbraith's book was never out of print since it surfaced as a bestseller. An explanation was required of the situation, and he felt that he had the wit and style to do so. .
I believe that if the author could synopsize the book it would consist of three sections. The events leading up to the collapse, up to chapter 7, were discussing the boom and its components as well as the elements of the disaster that was brewing on Wall Street. The middle section of the book discussed the crash itself, and its date, time, and immediate reaction from America. The ending section of the book was discussing the effects that the collapse had on Americans, future trading, and society as a whole. In a sentence, The Great Crash 1929 was an economical examination of the stock market collapse and its effects on the world over.
The discussions about the actual crash and thereafter were the only relevant sections of the book. They directly related to the event and the topic, not true of the beginning, which was a bit rambling and painful to read.