Earliest Union Among American Colonies 1643. Confederation of New England formed. John Marshall, Chief Justice of the Supreme Court later writes about this.
As the Connecticut Constitution was not only the first instrument of its kind, but also formed, in many respects, a pattern for others which became the organic laws of American States, so the first union of colonies, in 1643, is important not alone as being the first, but also as foreshadowing the later confederation and the final union of the States themselves. http://dld.bz/f8ch4
This union, the result of good-sense and of a judicious consideration of the real interests of the colonies, remained in force until their charters were dissolved. Rhode Island, at the instance of Massachusetts, was excluded; and her commissioners were not admitted into the congress of deputies, which formed the confederation.