9. Mexico
The U.S. invasion of Mexico is often remembered for the Mexican-American War (1846-1848), which resulted in vast territorial gains for the United States. Less known is the 1916-1917 Punitive Expedition, when General Pershing led American troops deep into northern Mexico in pursuit of revolutionary leader Pancho Villa. Though the expedition failed to capture Villa, it strained already tense U.S.-Mexico relations. These incursions echo other border conflicts, highlighting how security concerns and shifting alliances can quickly spill across frontiers, leaving lasting diplomatic scars.
