Wikipedia:Selected anniversaries/December 20
- 1803 – As part of the Louisiana Purchase (treaty pictured), New Orleans was transferred from France to the United States.
- 1917 – The Cheka, the first Soviet secret police, was founded. Felix Dzerzhinsky was appointed as its leader.
- 1988 – The United Nations Convention Against Illicit Traffic in Narcotic Drugs and Psychotropic Substances, a treaty mostly devoted to fighting organized crime by mandating cooperation in tracing and seizing drug-related assets, was signed in Vienna.
- 1995 – The NATO-led IFOR began peacekeeping in Bosnia and Herzegovina.
- 1999 – Portugal transferred sovereignty of Macau to the People's Republic of China.
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