If Osama wanted the US engulfed in race war, all he would have to do is get a white Chechen Muslim to assassinate Louis Farrakhan in public. The cities would be burning within an hour
And the cops mostly disappear or run away (as happened in LA during the last riots), or be ordered to not intervene (NYC and numerous other cities). In such a situation, citizens would need to defend their homes and neighborhoods (and don't think that just because you live in the suburbs, that the gangs can't drive to your area to trash it). In such a situation, the minimum requirement would be at least one gun, plus at least a thousand rounds of ammo for it (if you're going to keep them away by firing into the ground, you need enough ammo to keep doing this frequently over the course of 24-48 hours. If you're going to send the message across by having piles of bodies around your place, you can do with less ammo, but you are guaranteed of more hassle afterwards)