By what line of reasoning does George assert that America is not his country? What American document does George quote as justification for his position?

From the text:

I know very well that you’ve got the law on your side, and the power,” said George, bitterly. “You mean to take my wife to sell in New Orleans, and put my boy like a calf in a trader’s pen, and send Jim’s old mother to the brute that whipped and abused her before, because he couldn’t abuse her son. You want to send Jim and me back to be whipped and tortured, and ground down under the heels of them that you call masters; and your laws will bear you out in it,—more shame for you and them! But you haven’t got us. We don’t own your laws; we don’t own your country; we stand here as free, under God’s sky, as you are; and, by the great God that made us, we’ll fight for our liberty till we die.”

George stood out in fair sight, on the top of the rock, as he made his declaration of independence; the glow of dawn gave a flush to his swarthy cheek, and bitter indignation and despair gave fire to his dark eye; and, as if appealing from man to the justice of God, he raised his hand to heaven as he spoke.