| Term | Definition |
| Louisiana Purchase | Bought from France; doubled the size of the US (1803) |
| Lewis and Clark | Two explorers sent by Jefferson to explore the Louisiana Purchase |
| Marbury v. Madison | US Supreme Court case that established the principle of judicial review (1803) |
| Barbary pirates | Plundering pirates off the Mediterranean coast of Africa; President Thomas Jefferson’s refusal to pay them tribute to protect American ships sparked an undeclared naval war with North African nations |
| Chesapeake-Leopard affair | British warship fired on US warship off Virginia's coast, killing three Americans; resulted in high anti-British sentiment (1807) |
| Embargo Act | In response to impressment, this bill halted all foreign trade with disastrous economic consequences (1807) |