From the game manual:
In Gold of the Americas you play one of the four great colonial powers involved in the exploration and colonization of the New World. These were Spain, Portugal, England and France. Your job is to explore and colonize as much of the New World as possible for the greater glory of your Country and your King.
You have many enemies, and no friends. Your expeditions can be lost without trace, hostile natives or disease can wipe out your struggling colonies, privateers can loot your trading ships and of course the other players can launch raids and invasions against your territories. Worse still, any money that you manage to wrest from from this harsh environment is likely to be swallowed by a greedy King, whose tax rates are nothing less than extortionate.
However, there are compensations. Some activities put money directly into a special, privately maintained slush fund that is normally exempt from the tax-man's evil scrutiny. And if you are struggling with budgetary problems, you can always take it from other players with the aforementioned privateers, raids and invasions. Lastly, it is sometimes possible to manipulate the public purse.
Ultimately, success is measured by the development of your colonies. You have 30 turns (that's 300 years!) to establish your supremacy in the New World.