In 1492, Christopher Columbus set forth from Spain with the aim of discovering a direct navigable route from Europe to Asia. A direct navigable route between the two continents would have made intercontinental trade much easier. Columbus did not discover any such route, however, but instead accidentally "discovered" the American continent. He landed first on an island in what is now known as the Bahamas but which at the time was known as Guanahaní. When he returned to Spain, he wrote a letter to King Ferdinand and Queen Isabella of Spain to announce his discovery of the continent. This, ostensibly, was his main reason for writing the letter.
In his letter to the king and queen, Columbus also described the native people he met on the American continent. He noted that the indigenous people were "timid and full of terror." He also noted that they seemed to have no form of government and, significantly, that they were unarmed. He also suggested that because the native people were so timid and vulnerable, Spain might easily invade and conquer the territory. In fact, Columbus boasted that he had already taken possession of much of the land in Spain's name, simply by declaring that the land now belonged to Spain and planting the king's flag in the soil.
It is clear, therefore, that Columbus wrote this letter not only to inform the king and queen about a new land that he had discovered, but also to encourage them to invade and conquer the land for Spain.