The Japanese occupation of Manchuria was the first real test of the League of Nations, as this was exactly the kind of aggressive act the League was created to prevent. Unfortunately, the League failed the test.
Ever since the eighth planet, Neptune, was discovered in 1846, some astronomers searched for a hypothetical ninth planet. Clyde Tombaugh discovered the ninth planet in 1930. Or did he?
Japan had a rough time of it in the 1920s, between the global economic shocks and a devastating 1923 earthquake. Japanese military commanders saw control of Manchuria as key to Japan's economic independence, and they weren't about to let the politicians in Tokyo interfere.
Chiang Kai-shek unified China, more or less, but survival of the Nationalist government was threatened by warlords, the Japanese, and the Communists. Of these threats, Chiang regarded the Communists as the greatest.
The economic bad news had been centered in the United States, but in 1931, bank failures began multiplying in Europe, leading to the Great Depression.
The combination of higher reparations payments and a slower economy led the German government to pursue harsh and unpopular austerity policies.
The crash of the stock market was a shock, but what did it mean? No one was sure, but over the next 18 months, the US economy went from bad to worse.
There were voices warning that the stock market was overpriced, but even in October 1929, there were louder voices proclaiming that all was well, right up to the moment the bottom fell out of Wall Street.
By the beginning of the twentieth century, America already had a reputation for stock speculation, but the Roaring Twenties set new records.
Unusually heavy rainfall led to widespread flooding in the Mississippi Valley in 1927. The Coolidge Administration's Secretary of Everything, Herbert Hoover, was tasked with flood relief. What kind of relief you got depended heavily on your skin color.
Meanwhile, a different sort of flood was rising on the New York Stock Exchange.