- December 1: Tsar Alexander I of Russia dies, and his younger brother Nicholas I succeeds him.
- December 25: The Decembrist Revolt, an unsuccessful uprising of Russian military officers, takes place in Saint Petersburg.
1826
- February 24: The Treaty of Yandaboo ends the First Anglo-Burmese War, with Burma ceding the Tenasserim Coast and Arakan to the British.
- April 12: Agustín de Iturbide, the former emperor of Mexico, is executed after he returns from exile and attempts to reclaim the throne.
- July 4: Thomas Jefferson, John Adams, and James Monroe, three former presidents of the United States, die on the same day, which is the 50th anniversary of the Declaration of Independence.
1827
- February 6: The Treaty of London establishes an independent Kingdom of Greece under the protection of the United Kingdom, France, and Russia.
- October 20: The Battle of Navarino, a major naval battle of the Greek War of Independence, takes place between the Ottoman Empire and the allied fleets of the United Kingdom, France, and Russia. The allied forces are victorious, destroying Ottoman naval power and securing Greek independence.
1828
- January 22: The Russian army crosses the Danube River and invades the Ottoman Empire, starting the Russo-Turkish War (1828-1829).
- April 17: The USS Delaware becomes the first ship of the United States Navy to circumnavigate the Earth, completing a three-year voyage.
1829
- February 10: The Treaty of Adrianople ends the Russo-Turkish War, with the Ottoman Empire ceding territory to Russia and granting autonomy to Serbia, Wallachia, and Moldavia.
- September 14: The Adrianople Fire destroys much of the city of Adrianople (now Edirne, Turkey).
- December 20: The British East India Company signs the Treaty of Yandabo with Burma, ending the First Anglo-Burmese War.