Answer:
The 16th century saw the creation of the first large colonial empire by European powers. The empires of Spain and Portugal resulted from their sponsorship of the great voyages of discovery. In the case of Spain its empire would not have been created without the achievement of political unity at home. This came about in1469 when Isbella of Castile married Ferdinand of Aragon. With his support, she restored order and royal authority in Castile. In 1492 they completed the conquest of the Moorish kingdom of Granada, bringing to a conclusion the Reconquista, the reconquest of Islamic Spain.
The achievement of Ferdinand and Isabella rested on the cooperation of their two realms. Aragon feared being swallowed up by the far richer Castile and made little contribution to Spain's subsequent greatness. Yet the union was held together, first by Ferdinand and Isabella, and then from 1516 by the Hapsburgs, initally in the person of Charles V. Charles inherited both realms and was also elected Holy Roman Emperor in 1519. Spains incorporation into the Hapsburg Empire offered it the opportunity to use its own resources and those of its American empire on a much wider stage. Spain assumed the role of the leading power in Europe until well into the 17th century.
Following Columbus's successful voyage of 1492, Isabella needed to establish her right to colonise the Americas. After arbitration by the pope, Spain and Portugal came to an agreement at the Treaty of Tordesillas in 1493. All lands west of an imginary north to south line drawn 370 leagues west of the Azores and Cape Verde Islands were to go to Spain, and all those east of it to Portugal. The result of this was that Portugal got Brazil, and Spain virtually all the rest of South and Central America, and even parts of North America.
Work in progress