Earlier versions of Civilization V had a trade system, but the International Trade Route model that is implemented in Brave New World is an entirely new aspect of the game. You are now able to control foreign and domestic trade in ways that can make your empire wealthy, bigger, or stronger. Trade influences the spread of religion, and it helps you keep nations friendly—people like when you make them money. This section begins with the ways in which this system relates to the older trade model and goes on from there.
Civilization V: Brave New World Trade Routes