Your ultimate goal, as a global real estate mogul, is to accumulate the most wealth across all cities. You will reach this goal by progressively unlocking several cities, from Atlantic City to Paris to London, opening properties for business, and building and upgrading buildings to fill those properties.
The game starts with Atlantic City. Paris is the next destination, it unlocks when you reach City Level 6 in Atlantic City. Next is London! Unlocked by reaching City Level 12 in Paris.