Portugal gained control of the spice trade because of the country's strong presence on the water with its ships and naval command. Because of this, they were able to defeat the Muslims in the Indian Ocean and its control in the trade avenues.
In the 15th century, Portugal had a strong presence on the sea due to its established relationship with Africa. Through this relationship, they were able to transport a significant amount of gold from Africa to Europe. With this knowledge of the seas, they were able to gain power for the spice trade. In doing so, they completely transformed the way trade was conducted since they took away the cooperative structure that was common among African countries at the time.