In his persuasive writing, "The Crisis, Number I", by Thomas Paine, he refers to Great Britain as "a foreign dominion" to enforce the idea that the colonists are already a sovereign nation.
He wants to persuade people that the right thing to do is to free themselves from Great Britain. His purpose is to persuade the colonists to unite against Great Britain. He uses language that can be clearly understood by everyone so as to unite them and make them want to fight for their independence.