Which of these innovations was used in the Inca Empire and the Roman Empire?

The Romans built a Empire solely through conquest. And although the Inca led some military campaigns in the North, more kingdoms it annexed into its empire were through diplomacy and politics; convincing the neighboring kingdoms that joining the empire came with greater benefits then being independent.

The Roman empire was far larger than the Inca, consisting of about 55 of todays modern countries. The Inca consists of about 4 of todays modern countries. The Romans typically made enemies of everyone and struggled to defend their vast amount of territory. Even the dividing of the empire between East and West did little to combat ongoing war and rebellion. And unlike the Aztecs, the Inca were a pre-Columbian people that created an empire on mostly peacefully terms. Different kingdoms were not bothered by annexation because they were allowed to keep their religion, language and customs and basically live as they did before; the only difference was is that they had to give their loyalty to the Inca, as well as pay a tax.