米英戦争
米英戦争は主に3つの戦線で行われた。すべてインディアンの領土であり、地元のインディアンが米英両陣営の抗争に巻き込まれて虐殺されていった。アメリカは、英領カナダの奪取を狙い、カナダ領内に侵攻した。米英戦争2年目となる1813年5月にはナイアガラ川河口近くにあったイギリス軍のジョージ砦を攻撃して占領した。エリー湖、オンタリオ湖をおさえ、アッパー・カナダの制圧には成功するも、セント・ローレンス川の水運をおさえることはできず、結果モントリオール、ケベックの攻略は失敗し、ロウアー・カナダの制圧はできなかった。こうしてアメリカのカナダ侵略の野望は潰えた。
英米関係
In several episodes the American general Winfield Scott proved a sagacious diplomat by tamping down emotions and reaching acceptable compromises. Scott handled the "Caroline" affair in 1837. Rebels from British North America (now Ontario) fled to New York and used a small American ship called the "Caroline" to smuggle supplies into Canada after their rebellion was suppressed. In late 1837, Canadian militia crossed the border into the US and burned the ship, leading to diplomatic protests, a flare-up of Anglophobia, and other incidents.
Tensions on the vague Maine–New Brunswick boundary involved rival teams of lumberjacks in the bloodless Aroostook War of 1839. There was no shooting but both sides tried to uphold national honor and gain a few more miles of timber land. Each side had an old secret map that apparently showed the other side had the better legal case, so compromise was easily reached in the Webster–Ashburton Treaty of 1842, which settled the border in Maine and Minnesota. In 1859, the bloodless Pig War determined the question of where the border should be in relationship to the San Juan Islands and Gulf Islands. But, the Clayton–Bulwer Treaty proved to be an important step in improving relations.