You forgot tech and that time earlier in the year when we spent some time destroying some of ours after we felt we had picked up a bit too much and wanted to share the wealth.
You know, if we're bringing geography into this, my nation is all in the water. How do I have an army or tanks? Or infrastructure for that matter?
OH !@#$! I HAVE A NATION OF FROG PEOPLE!
I have marble/wheat, and if I wanted to, I could make some serious money with it. You've got two EXTREMELY high demand resources. Trust me, you can find trades.