What factor allowed the incas to use their military efficiently

The Inca Army was the military corps that ensured the expansion and consolidation of the Inca Empire.

This army was multi-ethnic and was in charge of defending the sovereignty of their lands, extending them and quelling rebellions. It was often also used for political interests such as coups d'état.

As the Inca sovereignty grew in size and population the army did it in the same way. The greatest concentrations of Inca warriors in the epochs of splendor of the empire came to make up about 200,000 soldiers in a single army (Huayna Cápac era).

The militarism that the Inca monarchy had made belonging to it, an important position. The soldiers were given food, clothing and state aid in replacements for their family in regard to the agricultural activity that the levado should be fulfilling, so that being a permanent warrior was not a bad charge and even occupied his own space in the political-social pyramid.

When they returned from a successful campaign to Cusco, children and women received them as heroes and a ceremony was held in honor of them.

where is the section with the question?

social contract theory, nearly as old as philosophy itself, is the view that persons' moral and/or political obligations are dependent upon a contract or agreement among them to form the society in which they live