It's roots predate Christianity to the time of the Greek and Roman empires.
Well, the point I'm trying to get at is that yes Christianity isn't necessarily tied to one ethnic group, and certainly not to the same extent that Islam is tied to Arabic or Judaism to Hebrew.
but in practice, in the United States and elsewhere, different ethnic groups compose different churches. Episcopalians typically can trace their ancestry to England, Southern Baptists are typically Scot-Irish, Lutherans are typically Nordic.
So when you see someone proclaiming that he's a true Christian and wants to tell everyone that he has been saved and he will stand up for the persecuted Christians, deep down inside I feel that it is simply an expression of the obstinate Scot-Irish spirit.