From Civ World
Economics is a type of Era victory.
Economic victories are won by amassing a target amount of gold, measured by adding all the treasuries of all the players in the Civilization. Whenever an Economic victory is won, the condition for the next Era will be a more difficult gold total.
The first and easiest Economic victory is to acquire 20,000 gold. Difficulty increases from there up to a maximum of 100,000,000, based on the frequency of Economic victories won.