John Green covers the Indus Valley Civilization in this Crash Course World History episode, working through the who, how, when, where, and why of a society that once covered a larger territory than Egypt or Mesopotamia. He walks through what actually counts as a civilization, then applies that checklist to cities like Mohenjo-daro, pointing out the grid-planned streets, covered drains, and standardized brick sizes that suggest centralized planning without any clear evidence of kings, palaces, or armies. The script pauses for an aside aimed at historians, and later Green digresses into blunt advice about relationships, both delivered with the show's usual rapid-fire humor. The back half of the episode sits with the Indus Valley's unsolved ending: no monumental collapse, no invasion recorded, just cities gradually abandoned, and historians left arguing over river shifts, climate change, or some quieter unraveling. Green treats the uncertainty as the point rather than a gap to paper over, closing on how much about this civilization, including its own writing system, still hasn't been deciphered.