Ah ah ^^ THIS ^^.
Only it is not true I suspect.
Learn your history and you will find something very similar happened to the Romans.
The barbarians were indeed invited and payed a salary as they partook in the army. They climbed up the social/hierarchical ladder (black emperor and all that) and devoured the system from within.
This should be a lesson to Europeans but alas it ain't.
This should also be a lesson to the Muricans as they tend to have a similar outlook on a multi racial equal opportunity empire as did the Romans, for similar reasons. Tough luck,it didn't work out in the end.