Europa Universalis IV

Like the description says accumulate 3000 gold, without spending them. The best way of earning money is by waging War, plundering enemy provinces, blocking their port and most importantly winning the war and claiming gold and tributes as reward. That is from a in game time point of view ie if you want 3000 as fast as possible and still have plenty of time doing other things. fast forward time can be quicker if you don't want to do as much work.

The Economy idea speed things up.