In the beginning of the game, I was slowly building up my treasury by 2 golds every turn. Then, all of a sudden, I received messages stating that treasury was dangerously low. I was at a hundred and some but now I had fallen to 0. I couldn't support a military, establish embassies or anything. I even filled my territory with roads but was still at -183 per turn. How do you go about working towards a huge treasury like in the thousands?