That was foremost in their mind.
The were worried about centralized power, which is why they started with the Articles of Confederation, instead of the Constitution.
Later realizing the need for greater centralized power in the form of a national government, they instituted the Constitution. But, they promised a Bill of Rights to follow, to protect the people from their own government which they had just instituted. The Bill of Rights didn't have anything to do with foreign powers.
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