Transcontinental Railroad: Completed in 1869, it connected the East Coast with the West Coast, revolutionizing transportation and trade.
Bleeding Kansas: A series of violent conflicts between pro-slavery and anti-slavery factions over whether Kansas would enter the Union as a free or slave state.
Dred Scott v. Sandford: A landmark Supreme Court case in 1857 that ruled enslaved African Americans were not citizens and could not sue for their freedom.