Portugal: Portugal was the first European kingdom to utilize travel using the sea route to explore travel and trade with other regions. The main reasons for Portugal taking this initiative was Portugal's lengthy seacoast, Portugal's excellent harbors and Prince Henry of Portugal who was very interested to spread Christianity in other parts of the world as well as improve his kingdom's profits via maritime activity. During the 16th century, the Indian Ocean (which was shared earlier by the Persians, Arabs and Indians) was dominated by the Portuguese because of the technological superiority of the Portuguese especially their weapons. The Portuguese even though had small ships, the cannons that were mounted on them proved superior to other boats and ships that they encountered in the Indian Ocean. The intention of the Portuguese was to spread Christianity indeed. But they were so committed to converting people of other regions into Christianity that they ended up in forced conversions or burning down mosques and therefore their intention to spread Christianity was not in a peaceful manner.
Portuguese school for navigation: The Portuguese set up a school for navigation which facilitated travel to and trade with West Africa and was instrumental in the creation of a global trading-post empire. Prince Henry of Portugal, started a school for navigation. Bartolomeu Dias and Vasco da Gama were the students of this school of Navigation.
Christopher Columbus's voyage: Queen Isabella and King Ferdinand of Spain funded Christopher Columbus's voyage Columbus used the Greek geographer Ptolemy's maps too. But Columbus was of the opinion that the voyage "west" was shorter than the Portuguese route from Europe around the tip of Africa and east. Thus, Queen Isabella and King Ferdinand of Spain funded Christopher Columbus's voyage to the “west” which was an alternate to the route taken by the Portuguese in their trade in the Indian Ocean.
Bartolomeu Dias: Bartolomeu Dias in 1488 sailed around the Cape of Good Hope from Portugal and returned back to Portugal after finding the southern tip of Africa.
Vasco da Gama: Vasco da Gama around 1497 sailed around the Cape of Good Hope and sailed to Calicut in India after crossing southern Swahili cities.