History often blames genocide solely on murderous demagogues and military campaigns. But more often than not, the forces that unleash ethnic cleansing arise slowly and during peacetime, and stem from seemingly everyday interactions in places that are home to diverse peoples. What sorts of exchanges and social conditions unleash genocidal behavior? How do people who long lived together as neighbors …

Massachusetts and Virginia became American states after colonists repelled an imperial power. But the area now known as New Mexico joined the Union when it was conquered by the U.S. Army. The U.S. incorporated the land after the Treaty of Guadalupe Hidalgo, but its inhabitants weren’t automatically U.S. citizens; their status became the subject of negotiations and controversies over who …

When it comes to picking the country’s presidents, the richest and most populous state hasn’t much mattered. Because their primaries are held earlier and they are swing states in the general election, smaller and colder places—like New Hampshire, Iowa, and Ohio—have an outsized influence on who occupies the White House. But could 2020 be different? California has moved its presidential …