To be clear, fear for one's life united every American, and has always done so. America wouldn't have gotten the support for world war if it wasn't for the american propaganda machine being in full swing. Now, to clarify, it's a damned good thing that it did because as much as I love German food, I'm not fond of slavery. Just make sure you understand that the motivations for humans working together is RARELY for the common good, it's almost exclusively for the common self.
I've drug myself up from my bootstraps the same as many people have had to do, and if America is great for a reason, it's because for the most part people stay out of your way when you try to do that, instead of clubbing you over the head and taking what's yours (that only happens after you make your first million). I can also acknowledge though that the dream of the white picket fence'd family comes at a cost to someone, whether it be within our country or without, and that those who created that image had the most to gain.
Finally, great Americans don't refer to themselves as such. If I were pressed to state the American virtue which is dead and buried, it would be humility.