The Treaty of Tordesillas was agreed upon by the Spanish and the Portuguese to clear up confusion on newly claimed land in the New World. The early 1400s brought about great advances in European exploration. In order make trade more efficient, Portugal attempted to find a direct water route to the India and China. By using a direct water route, Arab merchants, who owned land trade routes, were not able to make a profit off of the European trade merchants. After Columbus discovered the New World in 1492, it was clear that conflict would soon arise over land claims by Spain and Portugal. The Portuguese also wanted to protect their monopoly on the trade route to Africa and felt threatened. It was only after the realization that Columbus had found something big that land became the important issue. The newly discovered land held great potential wealth which would benefit European nations.
On May 4, 1493 Pope Alexander VI took action to clear up any confusion that may have arisen over territorial claims. He issued a decree which established an imaginary line running north and south through the mid-Atlantic, 100 leagues (480 km) from the Cape Verde islands. Spain would have possession of any unclaimed territories to the west of the line and Portugal would have possession of any unclaimed territory to the east of the line.
After further exploration, the Portuguese grew dissatisfied with the agreement when they realized how much more land Spain had been given. In June of 1494 the line was re-negotiated and the agreement was officially ratified during a meeting in the Spanish town of Tordesillas. The Treaty of Tordesillas re-established the line 370 leagues (1,770 km) west of the Cape Verde Islands.
It was evident that little exploration had taken place at the time the treaty was signed because Spain was granted a much larger portion of land. Portugal was only given possession of Brazil. Portugal pushed over the next several hundred years to move the border of Brazil westward. Because the line was not very well defined, the Spanish did not put up any opposition to this Portuguese expansion.Wapedia