What event led to increased aerospace and aeronautical research to

improve America's defense systems?

Who ever answers first gets ! trade in the vedic age led to a. the rise of kingdoms because of the importance of controlling land and long-distance travel routes b. the building of an extensive system of roads because of the difficult terrain c. the creation of a large banking class because of the need to exchange different currencies d. the development of a centralized government that controlled the economic decisions of its people