Up to this time the two major powers exploring the world were Spain and Portugal. These nations worried that their new territories would be taken by each other, or by others. In order to protect their new empires, these nations looked to the Pope for help.
In 1493, the Pope drew a line on the globe cutting the New World in half. This line was known as the Line of Demarcation. Any territory discovered on the east side of the line was to be controlled by Portugal, while any lands found on the west side of the line were to be ruled over by Spain.
In 1494, Spain and Portugal signed a treaty moving the line further west. This treaty was known as the Treaty of Tordesillas, and divided the New World between these two powers.
It is well to give when asked, but it is better to give unasked, through understanding.