Now, what factors create, at birth, natural allegiance to this country?
“It is an established maxim that birth is a criterion of allegiance. Birth however derives its force sometimes from place and sometimes from parentage, but in general place is the most certain criterion; it is what applies in the United States; it will therefore be unnecessary to investigate any other.” James Madison
A good point. When a child is born, and until it is much older, the child's allegiance is to it's family. It doesn't even comprehend the concept of "government" beyond that of it's father.
National allegiance is unknown at an early age, but paternal allegiance is understood quite quickly. As the twig is bent, the tree shall grow.