The Constitution the way I look at it is what made the USA officially a Republic. I would think the people of the time considered the colonies to be a collections of independent states united for the purpose of winning independence. Even after the Constitution was ratified there was a still a strong sense of states rights and the Tenth Amendment was taken a lot more seriously.
yes — another way to look at it is that before 1787-91 very few people in North America would have questioned the idea that any one or more of the 13 new “states” had every legal and moral right to strike out on their own as an independent nation
had any state declared itself completely independent of any connection at all with the others, declining to participate in any way with the Continental Congress at that time, I do not think there could have been any sense of imminent “civil war” (so long as that state did not attack any neighbors) .... others would have regarded that as unwise, dangerous etc. but few of that time would have thought “Pennsylvania has no RIGHT to go its own way”
sure, it was widely recognized that there were political, military, and economic benefits to cooperation, especially so long as Britain wanted to re-assert authority, but it would have been perfectly understandable to just about anyone across the 13 “states” if Virginia or New York or any state declared itself independent, sovereign, and completely free of all outside obligation and authority
that IS how it functioned until the constitution was adopted -— that Continental Congress could not command anyone to do anything
General Washington could not rely upon the slightest “national” support of the Continental Army -— all that could be done was to request and implore that the various states provide funds, supplies, troops......
of course there was an evolving idea of a potential nation.... but in 1776 there was neither a “government” of those united states of america nor was there hardly anyone who imagined that a “constitution” for such a government already existed