1924 — Edwin P. Hubble determines that stars in the Andromeda nebula are hundreds of thousands of light years beyond the Milky Way. This is conclusive proof that there are other galaxies besides our own.

Elsewhere that year:

• The Second Quota Law cuts immigration to half of the 1921 quota. It provides for a national origins plan to begin in 1929. The law also excludes all Asians, and is bitterly resented by the Japanese.
• J. Edgar Hoover becomes director of the Bureau of Investigation, renamed the Federal Bureau of Investigation in 1935.
• Lenin dies, and a power struggle begins within the Soviet Party for control of the government. Joseph Stalin, Lev Kamenev and Grigori Zinoviev for a triumvirate of successors against Leon Trotsky. Britain, France and Italy recognize the new Soviet regime.
• The Dawes Plan on German reparations goes into effect. It provides that reparation payments begin at one billion marks and rise over a period of four years to 2.5 billion marks per year.
• Congress passes an act making all native-born Indians full U.S. citizens.
• After a sensational trial, Nathan Leopold and Richard Loeb are sentenced to life in prison for the kidnapping of Bobby Franks. Leopold and Loeb, intelligent and well educated, apparently decided to kill someone just to see how it would feel and picked a young boy at random.