| 1920 | Foundation of the League of Nations | Created following the first World War in order to maintain peace. |
| 1921 | Establishment of the Communist Party of China | This marked the beginning of communist movements in China. |
| 1922 | Discovery of Insulin | This crucial medical discovery was made by Frederick Banting and Charles Best. |
| 1922 | Formation of the USSR | The Union of Soviet Socialist Republics (USSR) was created in Russia. |
| 1923 | Turkey becomes a Republic | Turkey was proclaimed a republic on October 29, after abolishing Ottoman Sultanate. |
| 1924 | Death of Lenin | The founder of the Russian Communist Party, Vladimir Lenin, died leading to a power struggle eventually won by Joseph Stalin. |
| 1925 | Invention of Television | John Logie Baird, a Scottish inventor, invents the first working television system. |
| 1926 | Queen Elizabeth II Born | The future Queen of the United Kingdom and other Commonwealth realms was born on April 21. |
| 1927 | Release of The Jazz Singer | The first feature-length motion picture with not only a synchronized recorded music score but also lip-synchronous singing and speech in several isolated sequences. |
| 1928 | Discovery of penicillin | Sir Alexander Fleming, a Scottish biologist and pharmacologist, discovered the world’s first broad-spectrum antibiotic, penicillin. |
| 1929 | Start of The Great Depression | Began with the Wall Street Crash in October, this was considered the most severe worldwide economic depression of the 20th century. |
