In 1916, Pancho Villa crossed the border to attack the US town of Columbus, NM. In retaliation, Woodrow Wilson ordered an American invasion of north Mexico - thereby dragging Washington into the Mexican Revolution (for the second time). It was notable for being the final time cavalry paid an important part in a US military action. Mexican history seems to do well, and we can also cover Pancho Villa's raid on Columbus - the last time anyone successfully invaded the continental US.