In August 1929, brokers had lent investors more than $8.5 billion to buy stocks, a sum greater than all the physical currency circulating in the United States. This episode examines the machinery behind the Wall Street crash rather than just its timeline. Beneath the boom of the 1920s, farmers were drowning in surpluses, factory wages had stagnated, and warehouses were filling with unsold goods. Yet investors kept buying on margin, encouraged by voices like Yale economist Irving Fisher, who declared that prices had reached a permanently high plateau.

The break came in late October. On Black Thursday the market shed 11 percent at the open and the ticker tape fell hours behind, leaving investors to sell blind. A bankers’ rescue staged on the trading floor held only through the weekend, and forced liquidations drove Black Monday and Black Tuesday. The episode then follows the damage outward: bank runs, a Federal Reserve that raised rates to defend the gold standard, crisis in Europe, and the reforms that still shape finance.

• Roger Babson warned in early September that a terrific crash was coming, and the press shrugged off the brief dip as the Babson break.
• Exchange vice president Richard Whitney walked the floor placing large bids for blue chips like U.S. Steel above the market price on behalf of the big banks.
• On October 29 more than 16 million shares changed hands and the ticker ran until almost 8 p.m.
• Nearly 2,300 banks failed in 1931 alone, and by the summer of 1932 the Dow had lost 89.2 percent of its peak value.
• Milton Friedman and Anna Schwartz blamed the Depression on the banking collapse and Federal Reserve policy more than on the crash itself, and the Dow did not regain its 1929 high until November 1954.