The key idea is recognizing a civilization that unified engineering, craft, and governance across a vast empire. The Incas match all the listed contributions: they built an extensive road system across the Andes that connected far-flung regions and supported military and civilian movement; they engineered irrigation and terrace farming to sustain large populations; their architecture featured impressive stonework in places like Machu Picchu; they practiced metallurgy, producing metal goods; and they created pottery and especially textiles and clothing that reflected their skilled craftsmanship. Plus, they maintained a centralized administrative and military structure to keep the empire organized. Mayans contributed in pottery, architecture, and textiles and built impressive cities, but their road and irrigation networks were not as expansive or centralized. Mongolians are renowned for mobility and military organization but not for the same scale of architectural engineering, irrigation, and centralized governance. The Tea Act is not a civilization at all.