The stop sign can be added to the list of empire-killing technologies. Taken together, they have had a formidable effect. Synthetics diminished the great powers’ need for strategic raw materials by offering substitutes. Aviation, cryptography, radio, and satellites, meanwhile, enabled those powers to run secure transportation and communication networks without worrying about contiguous territorial access. Innovations in medicine and engineering—such as DDT, antimalarials, plastic-based packaging, and “world-proofed” electronic equipment—further reduced the need for territorial control. They allowed objects and humans to safely travel to hostile terrains, meaning that colonizers didn’t have to soften the ground beforehand.