New World gold provided the economic basis for even more rapid European expansion.

When the New World came to be viewed by the hungry capitalists as having a potential for agricultural exploitation, New World labor needs expanded astronomically.
At first these needs were filled by surplus labor from Europe or by exploiting the local Indian populations.

When these labor sources proved to be inadequate, the exploitation of slave labor from Africa was the obvious answer.
While the Portuguese were the first to reach the shores of West Africa and the first to bring African slaves back to Europe, neither they nor the Spaniards ever dominated the slave trade which followed.

In 1493, as European exploration of the world moved into high gear, the Pope published a Bull dividing the world yet to be explored into two parts.
His intention was to limit competition and conflict between the rulers of Spain and Portugal and to prevent undue hostility between his two main supporters.
However, this left the other European powers, officially, with no room for overseas expansion.

While these powers refused to acknowledge the legality of the Bull and soon became involved in exploration and colonization in spite of it, they also tended to become more involved than did Portugal or Spain in some of the by-products of colonization, such as the slave trade.