Which technological advancement helped unify the Roman and Inca empires?

The technological advancement that helped unify both the Roman and Inca empires, though in different periods and regions, was the development and implementation of extensive road networks. For the Romans, it was their sophisticated system of roads, the famous Roman roads; for the Incas, it was the Qhapaq Ñan, also known as the Inca Trail.

Roman roads were constructed for military logistics initially but eventually facilitated trade, administration, and cultural assimilation across the vast Roman Empire, unifying diverse communities under Roman governance. They were engineered to be durable and spanned thousands of miles, often featuring stone layers, drainage systems, and bridges.

The Inca roads, meanwhile, consisted of a 40,000-kilometer network that connected various parts of the empire in the mountainous topography of South America. Much like the Roman roads, the Inca trails enabled the movement of armies, goods, and information across long distances, integrating various parts of the empire and permitting efficient administration.

Both road systems were remarkable feats of engineering for their time and key infrastructural elements that supported the unification and maintenance of their respective empires.