Complex sentence: Second, Spain wanted to use the islands' geographical location to trade with China and Japan and to spread Catholicism to those advanced civilisations, and the third was for Spain to spread Catholicism in the archipelago itself.
Split into simpler sentences: Second, Spain wanted to use the islands' geographical location to trade with China and Japan and to spread their religious belief to those advanced civilizations. Third was for Spain to spread Catholicism in the archipelago itself.