James Marshall spotted flecks of gold in the American River at Sutter's Mill, California, triggering the frenzy that became the Gold Rush.

Karl Marx and Friedrich Engels published The Communist Manifesto in London, weeks before revolutions swept across Europe.

The Treaty of Guadalupe Hidalgo ended the Mexican-American War, forcing Mexico to cede over half its territory to the United States.

Mexico and the United States signed the treaty ending the Mexican-American War, transferring vast territories including California and New Mexico to the U.S.

Karl Marx and Friedrich Engels published 'The Communist Manifesto' in London, laying out a theory of class struggle that would shape the next century of world politics.

Revolutionary crowds clashed with troops in Vienna, forcing the resignation of Chancellor Metternich, architect of Europe's conservative order for over three decades.