The Treaty of Tordesillas was the result of discussions concluded on June 7, 1494, during the years of Iberian
. It was subsequently ratified by Spain on July 2 and by Portugal on September 5 of the same year, and sanctioned by Pope Julius II
King Ferdinand and Queen Isabella of Spain and King John II of Portugal, mediated by Don Enrique Enriques, Don Gutierre de Cardenas and Doctor Rodrigo Maldonado, among others, decided to settle prospective conflicting territorial claims by establishing a boundary 370 leagues west of the Cape Verde Islands (46 degrees, 37 minutes of longitude west of the Prime Meridian) that circled the globe. The world would be split along this line, with non-Christian lands to the west becoming the property of Spain, and those to the east belonging to Portugal. In addition, ships of both nations would be allowed to sail anywhere within each other's waters.
This was a modification of the demarcation established by the Spanish-born Pope Alexander VI in the Bull Inter Caetera of May 1493. The pope placed the bisection of the earth's surface at 100 leagues west of the Cape Verde Islands, thereby awarding the entire New World to Spain and Africa and India to Portugal, a decision with which Portugal was not altogether pleased.
The line established by the Treaty of Tordesillas lay a few hundred miles inland in what is now Brazil at its deepest penetration into the South American continent. King John II thought he was improving his nation's position greatly, but it seems that nobody realized until later that so much of the New World had been effectively awarded to Spain. This included the advanced and rich, albeit brutal, civilization of the Aztecs, which the Spaniards decimated with, among other things, smallpox, horses and gunpowder, leaving quite a bit of gold lying around that was promptly shipped back to the Old World.
The influence of the Treaty of Tordesillas has been significant; though the line effected by the Treaty was nebulous for a long time, as problems determining exact longitude persisted for centuries. Simply consider that the official language of Brazil is Portuguese while basically every other Latin American and Caribbean nation has Spanish as its main tongue.
Though neither Spain nor Portugal any longer has a claim to sovereignty over any of the lands divvyed up by them over 500 years ago (I think), the descendants of the conquistadors and other settlers certainly heavily shaped the history of the southern continent of the Western Hemisphere, and will continue to do so for many years.