Magellan's circumnavigation of the Earth (1519-21)
Despite what you have seen in older media, the populous during the age of exploration believed the earth was round. If this was proven true, then a western route to the Spice Islands could be made by Spain. The search for spices was essential for Europe as spice like cinnamon were worth their weight in gold as they only grew in the far east and anyone with a grasp on the trade were guaranteed an immense fortune! Enter Ferdinand Magellan, a Portuguese sailor and navigator who renounced his citizenship to Portugal after his plans for the very route Spain needed was declined by the Portuguese monarch. With help from a slave of his named Enrique of Malacca who was enslaved by Magellan on a previous expedition to Malacca, Magellan was given 5 ships called Carracks.
Magellan knew the location of the East Indies including the Spice Islands (the Moluccas) prior to the trip, it was just a matter of finding the fastest western route to them was the question. On the journey, he traded with the indigenous of what is now modern day Brazil and set up a restbite camp at Port San Julian in what is now Argentina. He lost 2 ships while going through the Strait of Magellan at the south of the South American continent. Santiago was shipwrecked while the San Antonio deserted Magellan and returned to Spain. Magellan is the reason why the Pacific Ocean is called Pacific as he found the tremendous ocean placid and gentle in comparison to the Atlantic. He sailed the pacific for 99 days and stopped to resupply in what is now Guam. His landing in Guam is the first European documentation of Guam.
The Philippines at that moment in time was just an archipelago of various independent sultanates, kingdoms and principalities. Upon arriving in the Philippines, Magellan converted some of the natives and their king to Christianity. As Spain was and still is a Catholic country, the natives Magellan converted became Catholics. The king decided to pull a sectarian move and declared war on the Mactan, another indigenous tribe who were nearby as they weren't christains which led to a battle where Magellan sided with the indigenous king. A poison led arrow struck and killed Magellan, without ever having reached the Mactan Islands. The crew also lost the Concepcion which was destroyed due to lack of crew members and the Trinidad which stayed in the Philippines for repairs after being struck by a Portuguese vessel. Sebastián de Elcano and the surviving crew carried on (along with Enrique) where they made it to the Mactan Islands before continuing to circumnavigate the globe. When they returned to Spain, they confirmed the populous belief of the earth being round as well as bringing home the spices.