They wanted to colonize it, because more land meant more power. Also, the New World had items they could trade with China, specifically silver. One major find in the New World was Potosi, a mountain filled with silver, which China really wanted. Before, they had nothing to trade with China, but now they did. They also wanted other precious metals such as gold.
To find riches ;
The Spanish explored the New World in the early 1500s primarily for wealth, territorial expansion, the spread of Christianity, competition with other European powers, and to discover new trade routes. The discovery of silver mines like Potosi significantly fueled their interest in colonization. Additionally, personal ambition drove many explorers to seek fame and glory through their conquests.
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