4th January » Samuel Colt sells his first revolver pistol to the United States government.
13th January » The Treaty of Cahuenga ends the Mexican–American War in California.
16th January » John C. Frémont is appointed List of Governors of California e.g Governor of the new California Territory.
30th January » Yerba Buena, California is renamed San Francisco.
19th February » The first group of rescuers reaches the Donner Party.
22nd February » Mexican–American War: The Battle of Buena Vista 5,000 American troops defeat 15,000 Mexico e.g Mexicans.
23rd February » Mexican–American War: Battle of Buena Vista In Mexico, American troops under future president General Zachary Taylor defeat Mexican General Antonio López de Santa Anna.
1st March » The state of Michigan formally abolishes capital punishment.
9th March » Mexican–American War: The first large-scale amphibious assault in U.S. history is launched in the Siege of Veracruz.
29th March » Mexican–American War: United States forces led by General Winfield Scott take Veracruz (city) called Veracruz after a Siege of Veracruz or siege.
5th April » Birkenhead Park, the first civic public park in Britain, is opened in Birkenhead.
16th April » The accidental shooting of a Māori people named Māori by an England known as English sailor results in the opening of the Wanganui Campaign of the New Zealand land wars.
25th April » The last survivors of the Donner Party are out of the wilderness.
7th May » The American Medical Association is founded in Philadelphia.
6th September » Henry David Thoreau leaves Walden Pond and moves in with Ralph Waldo Emerson and his family in Concord, Massachusetts.
12th September » Mexican–American War: the Battle of Chapultepec begins.
13th September » Mexican–American War: Six teenage military cadets known as Niños Héroes die defending Chapultepec Castle in the Battle of Chapultepec. American troops under General Winfield Scott capture Mexico City in the Mexican–American War.
14th September » Mexican–American War: Winfield Scott captures Mexico City.
1st October » German inventor and industrialist Werner von Siemens founds Siemens AG & Halske.
4th November » Sir James Young Simpson, a British people called British physician, discovers the anaesthetic properties of chloroform.
10th November » The passenger ship 'Stephen Whitney (ship) or Stephen Whitney' is wrecked in thick fog off the southern coast of Ireland, killing 92 of the 110 on board. The disaster results in the construction of the Fastnet Rock or Fastnet Rock lighthouse.
19th November » The second Canada called Canadian railway line, the Montreal and Lachine, Quebec or Lachine Railway, is opened.
29th November » The Sonderbund is defeated by the joint forces of other Switzerland known as Swiss cantons under General Guillaume-Henri Dufour.
29th November » Whitman Massacre: Missionaries Dr. Marcus Whitman, his wife Narcissa, and 15 others are killed by Cayuse and Umatilla Indians, causing the Cayuse War.
5th December » Jefferson Davis is elected to the U.S. senate, his first political post.