Answer: In the case of Africa, Portugal wanted to establish a direct commercial route between this country and Asia and in the way it ws found the African continent was rich in natural resources. In the case of South America, to look for gold and establish new colonies.
During the fifteenth century the commercial route of spices from India (Asia) to Europe was monopolized by the Arabs, resulting in a more expensive purchase of spices for Portugal.
So, Portugal decided to carry out an exploratory expedition to these Indian lands and inaugurate a new commercial route by reaching the Indian Ocean by crossing the southern tip of Africa through the Atlantic Ocean. After this, explorations in the occidental coast of Africa began with the discovery of the existence of gold in these lands
Then, with the news about the discovery of lands by Columbus in the name of the Spanish Kings, Portugal decided to explore the now called Southamerica and exploit the resources.