The Portuguese King John II was not pleased with that arrangement, feeling that it gave him far too little land - it prevented him from possessing India. As of 1493, Portuguese explorers had only reached the east coast of Africa. He opened negotiations with King Ferdinand and Queen Isabella of Spain to move the line to the west and allow him to claim newly discovered lands east of the line. This resulted in the Treaty of Tordesillas of 1494. Very little of the newly divided area had actually been explored by Europeans, as it was only divided by the treaty, through which Spain gained lands including most of the Americas. The easternmost part of current Brazil was granted to Portugal when Pedro Álvares Cabral landed there while he was en-route to India.

Even though the treaty was negotiated without consulting the Pope, the resulting line is known as the Papal Line of Demarcation. In fact, the treaty effectively countered the bulls of Alexander VI and in the end it was sanctioned by Pope Julius II by his bull Ea quae of 24 January 1506.

Magellan was born around 1480 near Porto, in Portugal. After the death of his parents during his tenth year he became a page to Queen Leonor at the Portuguese royal court because of his family's heritage.

In March 1505, at the age of 25, Magellan enlisted in the fleet of 22 ships sent to host Francisco de Almeida as the first viceroy of Portuguese India. He remained there eight years, staying in Goa, Cochin and Quilon. He participated in several battles, later sailed under Diogo Lopes de Sequeira in the first Portuguese embassy to Malacca in today's Malaysia. In September, after arriving at Malacca, the expedition fell victim to a conspiracy ending in retreat.
In 1511, under the new governor Afonso de Albuquerque, Magellan and Serrão participated in the military occupation of Malacca. Following the defeat of the Malacca Sultanate their ways parted: Magellan was promoted, and returned to Portugal in 1512. Serrão departed on an expedition sent to find the "Spice Islands" in the Moluccas, where he remained for a while, becoming a military advisor to the Sultan of Ternate. His letters to Magellan would prove decisive, giving information about the spice-producing territories.
In the meantime, back in Portugal, Magellan had fallen out of favour to the royal court. In 1517 after a quarrel with King Manuel I, who denied his persistent demands to lead an expedition to reach the spice islands from the east, he left for Spain. He settled in Seville, married and devoted himself to studying the most recent charts, investigating, in partnership with cosmographer Rui Faleiro, a gateway from the Atlantic to the South Pacific and the possibility to reach the Moluccas, being Spanish according to the demarcation of the Treaty of Tordesillas.

Magellan and Rui Faleiro, offered their services to King Charles I - the later, Emperor Charles V and proposed the plan of sailing west to give practical proof of their claim that the wealth-promising "Spice Islands" lay west of the line of demarcation - that is, within the Spanish, not the Portuguese, hemisphere.

On March 22, 1518, their proposal received royal assent; they were appointed joint captains general of an expedition directed to seek an all-Spanish route to the Moluccas. Magellan was convinced that he would lead his ships from the Atlantic to the "Sea of the South" by discovering a strait through Tierra Firme. This idea did not originate with him; others had sought a passage by which vessels sailing continuously westward would reach the East and thus avoid the Cape of Good Hope, which was controlled by the Portuguese. In the royal agreement Magellan and Faleiro were directed to find "the" strait.
The expedition was funded largely by the Spanish Crown and provided with ships carrying supplies for two years of travel. Expert cartographer Jorge Reinel and Diogo Ribeiro, a Portuguese who had started working for Charles V in 1518 as a cartographer, took part in the development of the maps to be used in the travel. Several problems arose during the preparation of the trip, including lack of money, the king of Portugal trying to stop them, Magellan and other Portuguese incurring suspicion from the Spanish and the difficult nature of Faleiro. Finally, thanks to the tenacity of Magellan, the expedition was ready. Through the bishop Juan Rodríguez de Fonseca they obtained the participation of merchant Christopher de Haro, who provided a quarter of the funds and goods to barter. On the verge of departure, an attack of insanity prevented Faleiro from sailing with the expedition.

The fleet was provided by King Charles V and included five ships: the flagship Trinidad (110 tons, crew 55), under Magellan's command; San Antonio (120 tons, crew 60) commanded by Juan de Cartagena; Concepcion (90 tons, crew 45) commanded by Gaspar de Quesada; Santiago (75 tons, crew 32) commanded by Juan Serrano; and Victoria (85 tons, crew 43), named after the church of Santa Maria de la Victoria de Triana, where Magellan took an oath of allegiance to Charles V.

On 10 August 1519, the five ships under Magellan's command left Seville and descended the Guadalquivir River to Sanlúcar de Barrameda, at the mouth of the river. There they remained more than five weeks, finally setting sail on 20 September.

King Manuel I ordered a Portuguese naval detachment to pursue Magellan, but Magellan avoided them. After stopping at the Canary Islands, Magellan arrived at Cape Verde, where he set course for Cape St. Augustine in Brazil. On 27 November the expedition crossed the equator; on 6 December they sighted the coast of South America.
As Brazil was Portuguese territory, Magellan avoided it and on 13 December the fleet anchored near present-day Rio de Janeiro. There the ships were resupplied, but bad weather conditions caused them to delay. Afterwards, they continued to sail south along South America's east coast, looking for the strait that Magellan believed would lead to the Spice Islands. The fleet reached Río de la Plata on 10 January 1520. On 30 March the crew established a settlement they called Puerto San Julian (now in Argentina). On Easter day at midnight two Spanish captains led a mutiny against the Portuguese commander, which was unsuccessful because most of the crew remained loyal. Magellan with resolution, ruthlessness, and daring quelled it, executing one of the captains and leaving another to his fate ashore when, on Aug. 24, 1520, the fleet left St. Julian.

After reaching the mouth of the Santa Cruz, the Santiago was sent down the coast on a scouting expedition and was wrecked in a sudden storm. All of its crew survived and were rescued. At 52°S latitude on 21 October the fleet reached Cape Virgenes and concluded they had found the passage, because the waters were brine and deep inland. Four ships began an arduous trip through the 370-mile long passage that Magellan called the "Estrecho de Todos los Santos", because the fleet travelled through it on 1 November or All Saints' Day. The strait is now named the "Strait of Magellan". Magellan first assigned Concepcion and San Antonio to explore the strait, but the latter, commanded by Gómez, deserted and returned to Spain on 20 November.

On 28 November the three remaining ships finally, entered the South Pacific. Magellan named the waters the "Mar Pacifico" because of its apparent stillness. His crew were the first European to reach Tierra del Fuego just east of the Pacific side of the strait.

Tortured by thirst, stricken by scurvy, feeding on rat-fouled biscuits, finally reduced to eating the leather off the yardarms, the crews, driven first by the Peru Current and throughout the voyage by the relentless determination of Magellan, made the great crossing of the Pacific. Until December 18 they had sailed near the Chilean coast; then Magellan took a course northwestward; not until Jan. 24, 1521, was land sighted, probably Pukapuka in the Tuamotu Archipelago. Crossing the equinoctial line at approximately 158°W on February 13, the voyagers on March 6. made first landfall at Guam in the Marianas, where they obtained fresh food for the first time in 99 days. A Memorial, sent by Magellan to King Charles before leaving Spain, suggests that he knew (probably partly from Serrco's letters) the approximate position of the Moluccas; in sailing now to the Philippines instead of direct to the Spice Islands, he was doubtless dominated by the idea of early revictualling and the advantage of securing a base before visiting the Moluccas.

Leaving on March 9, Magellan steered west-southwestward to a group of islands later called the Philippines. On 17 March Magellan reached the island of Homonhon in the Philippines, with 150 crew left. At Massava he secured the first alliance in the Pacific for Spain, at Cebz the conversion to Christianity of the ruler and his chief men. Less than two months later, however, Magellan was killed in a fight with natives on Mactan Island on the morning of 27 April 1521.

The casualties suffered in the Philippines left the expedition with too few men to sail all three of the remaining ships. Consequently, on 2 May, they abandoned Concepción and burned the ship. The fleet, reduced to Trinidad and Victoria, fled westward to Palawan. They left that island on 21 June and were guided to Brunei, Borneo by Moro pilots who could navigate the shallow seas. They anchored off the Brunei breakwater for 35 days, where they witnessed the golden splendour of Rajah Siripada's court with such things as porcelain and eyeglasses, both of which only just becoming available in Europe. And they discovered cloves, which were to prove even more valuable than gold, upon their return to Spain.

After reaching the Maluku Islands - the "Spice Islands" - on 6 November, only 115 crew were left. They managed to trade with the Sultan of Tidore, a rival of the Sultan of Ternate, who was the ally of the Portuguese. The two remaining ships, were laden with valuable spices such as cloves and cinnamon, and planned to return to Spain by sailing further westwards along the Portuguese trading territories. However, at leaving Tidore, the Trinidad began to take on water. The crew tried to discover and repair the leak, but failed. They concluded that Trinidad would need to spend considerable time being overhauled, but the small Victoria was not large enough to accommodate all the surviving crew. So they settled that the Victoria should depart with part of the remaining crew and sail further west bearing for Timor, Java and Cape of Good Hope to reach Spain.
About twenty weeks later, in April 1522, the newly repaired Trinidad departed also but attempted to return to Spain via the Pacific route, the way they had come. This attempt failed. The undermanned Trinidad was captured by the Portuguese in Maluco, and was eventually wrecked in a storm while at anchor under Portuguese arrest. Its crew was jailed by the Portuguese, and only four men later returned to Spain.

The Victoria set sail for Spain via the Indian Ocean route on 21 December 1521, commanded by Juan Sebastián Elcano. They managed to elude the Portuguese while sailing enemy trade routes in the Indian Ocean and rounded the Cape of Good Hope by 6 May 1522. Unfavourable winds and rapidly diminishing supplies, led to many of the crew dying of starvation and scurvy. Twenty crewmen died before Elcano made landfall on Cape Verde, a Portuguese holding, where on 9 July he had to abandon 13 more crew in Portuguese imprisonment in fear of losing his cargo of 26 tons of spices.
On 6 September 1522, Elcano and the remaining 18-man crew of Magellan's voyage arrived in Spain aboard the last ship in the fleet, Victoria, almost exactly three years after they departed. Magellan had not intended to circumnavigate the world, only to find a secure way through which the Spanish ships could navigate to the Spice Islands; it was Elcano who, after Magellan's death, decided to push westward, thereby completing the first voyage around the globe.