I don't get it. Here I am, the Iroquois. I'm trying a diplomatic approach instead of the old warmongering me, I've only declared war once by military alliance on the already crushed Americans to get me some Incan luxuries. I thought everything was great, and when I was nearing the end of the Ancient Age, my Iron depleted. I had to pay the powerful Incans next door every 5 turns so they DON'T murder my spearmen with their knights. (I have no horses either). Now when we get Steam Power, not only do I have to trade for Coal, but I need to trade for some Iron as well, just so I can rail my whole civ together . . . in twenty turns. By the time I finished, there was one turn left and I had about 20 workers on the job. I couldn't wait to get Nationalism to overpower the threat of the Inca. I finally did, and it cost me 2000 gold to upgrade my spears. Which I easily got by setting my Science Slider to 0%. Now I'm in the mid Industrial Age around 1800AD (perfect timing, the first time I hit the Idustiral Age so early) and I have the only supply of Rubber!!! Upgrading all my men to Infantry was easy and now I'm the wonder of the world (that is, assuming it doesn't deplete as well). Thanks to Smith's Trading, I'm richer than ever. I might actually see the United Nations for the first time. But anyway the question is, why do resources deplete? I work so hard for that Iron and it just goes away.