Important dates in U. S. history By Malec123 Jul 8, 1787 1780s: Constitution of the United States of America (1787) https://www.britannica.com/list/25-decade-defining-events-in-us-history Nov 21, 1794 1790s: Whiskey Rebellion (1794) https://www.britannica.com/list/25-decade-defining-events-in-us-history Aug 1, 1803 1800s: Louisiana Purchase (1803) https://www.britannica.com/list/25-decade-defining-events-in-us-history Sep 21, 1815 1810s: Battle of New Orleans (1815) https://www.britannica.com/list/25-decade-defining-events-in-us-history Jul 16, 1823 1820s: Monroe Doctrine (1823) https://www.britannica.com/list/25-decade-defining-events-in-us-history Sep 3, 1829 1830s: Era of the Common Man (1829–37) https://www.britannica.com/list/25-decade-defining-events-in-us-history Jun 28, 1848 1840s: Treaty of Guadalupe Hidalgo (1848) https://www.britannica.com/list/25-decade-defining-events-in-us-history Aug 7, 1857 1850s: Dred Scott Decision (1857) https://www.britannica.com/list/25-decade-defining-events-in-us-history Aug 1, 1863 1860s: Battle of Gettysburg (1863) https://www.britannica.com/list/25-decade-defining-events-in-us-history Nov 7, 1876 1870s: Battle of the Little Bighorn (1876) https://www.britannica.com/list/25-decade-defining-events-in-us-history