If as writing Spanish Conquistadors, would it have to be capitalized?

how about
European Explorers?

Neither conquistadors nor explorers is capitalized.

Europeans is always capitalized.

Thank you

You're welcome.

and how about europeans in general

When it comes to capitalization, there are certain rules to follow. In general, proper nouns and proper adjectives are capitalized. Let's apply these rules to your examples:

1. Spanish Conquistadors: In this case, "Spanish" is a proper adjective, as it refers to both the nationality and the specific group of conquerors. "Conquistadors" is a common noun, but since it is part of the title, it is also considered a proper noun. Therefore, both "Spanish" and "Conquistadors" should be capitalized: "Spanish Conquistadors."

2. European Explorers: Here, "European" is a proper adjective referring to a specific group of explorers. "Explorers" is a common noun, but since it is part of the title, it is also considered a proper noun. Hence, both "European" and "Explorers" should be capitalized: "European Explorers."

In summary, both "Spanish Conquistadors" and "European Explorers" should have capital letters.