Alliance means when two countries becomes friends or are associated. It's like partnership.
They were referred to as "Royal Colonies"; it's a term with British origins means those territories not annexed yet under its control.
The correct option is D.
The development of agriculture opened the way of civilization for native Americans in Mexico and South America. The cultivation of maize in large quantity especially brought about trading with neighboring cities and towns and open up irrigation system and increased the population density of Mexico and South America.
