The Seven Cities of Gold (1984) by Ozark Softscape.
If you’re from the older generation and enjoyed classics like M.U.L.E., Elite, or Pirates, I'm pretty sure you also played this little gem.
It's an open-world strategy game designed by Danielle Bunten Berry (one of the masterminds behind M.U.L.E. the year before). You take on the role of a 15th-century Spanish explorer sponsored by the Crown.
You sail from Spain to the New World - either a detailed historical map of the Americas or a random one - with ships, a crew, some gold, and trade goods.
Your goal is straightforward (but far from easy): explore unknown lands, map coastlines and rivers, discover native settlements, trade or conquer for gold, and establish forts or missions. That, in a nutshell, is the core of the game.
You can return to Spain at any time to earn promotions, titles, and sponsorship for even better expeditions. One of the most interesting aspects was your interaction with the natives, which could range from peaceful trade to bloody conflict. Your "moral" choices actually affected the outcome - not quite to the same degree as in Ultima IV but still noticable...
One thing that I always wondered about was the small screen (C64 version) - I assume there might have been software or hardware limitations?