{"method":"Benchmark years are used for the first public atlas layer so that uncertain historical boundaries, cultural zones, population estimates, and event layers are not falsely presented as continuous exact annual reconstruction.","periods":[{"label":"Early urban worlds","scope":"Egypt, Mesopotamia, Indus, early state formation","year":-3000},{"label":"Late Bronze Age transition","scope":"Eastern Mediterranean, Near East, early imperial systems","year":-1200},{"label":"Classical world","scope":"Achaemenid, Greek, Indian, Chinese and Mediterranean worlds","year":-500},{"label":"Imperial ancient world","scope":"Roman, Han, Parthian and connected Afro-Eurasian routes","year":0},{"label":"Late antique transition","scope":"post-Roman West, Byzantium, Sasanian world, Gupta aftermath","year":500},{"label":"Early Islamic and Tang era","scope":"Abbasid, Tang, Byzantine, steppe and Indian Ocean systems","year":750},{"label":"Medieval consolidation","scope":"Byzantium, Islamic worlds, Song China, medieval Europe, African states","year":1000},{"label":"High medieval world","scope":"trade routes, universities, empires and religious geographies","year":1200},{"label":"Mongol and connected Eurasia","scope":"Mongol successor polities and transcontinental exchange","year":1300},{"label":"Late medieval / early oceanic transition","scope":"pre-Columbian Americas, Ottoman expansion, Ming, Indian Ocean","year":1450},{"label":"Early modern opening","scope":"Atlantic, Ottoman, Safavid, Mughal, Ming, European maritime expansion","year":1500},{"label":"Early modern empires","scope":"global maritime routes, gunpowder empires, colonial systems","year":1600},{"label":"Imperial competition","scope":"Atlantic empires, Eurasian states, trade companies","year":1700},{"label":"Revolutionary and imperial world","scope":"Napoleonic era, colonial expansion, industrial transition","year":1800},{"label":"Modern international-system baseline","scope":"CShapes-compatible global state boundaries begin","year":1886},{"label":"First World War opening","scope":"AP WWI atlas handoff","year":1914},{"label":"Second World War opening","scope":"AP WWII atlas handoff","year":1939},{"label":"Postwar settlement","scope":"UN order, decolonization baseline","year":1945},{"label":"Post-Soviet transition","scope":"post-Cold War state system","year":1991},{"label":"Contemporary atlas frame","scope":"AP current conflict, transport, displacement and disaster layers","year":2026}],"title":"AP World History Atlas benchmark periods","version":"2026-06-23-world-history-atlas-periods-v1"}