Because the countries banned are irrelevant and America, or hell the rest of the world would lose nothing if they got banned or something. He probably do this just to placate his supporters. I mean I can't think anything worthwhile coming out of Sudan or Somalia.
I always picked the small nations in South America first and then slowly works my way around the continent while avoiding to accidentally press anything in the American intervention pop up.
Eh, I always hated the concept of natural disaster in city building game. Just my personal feeling, I feels that it's just some gimmick from Simcity series that every dev feels need to follow. But well, I can see the reason why people enjoys them, each for everyone or something like that.
They're only useful when all of your army is wiped clean and the enemy is currently kicking you in the curb. Basically I only ever use to hurt my enemy out of spite.