Earlier quoted context omitted.
The framers didn’t anticipate armies becoming permanent institutions, which is why we have a “no standing army” requirement that we just kind of ignore. But even that only makes the second amendment clearer: if you don’t have a standing army, who has the guns? The answer is militias comprised of heavily armed citizenry.
I am pretty certain that the large military powers at the time (England, France certainly Prussia) had standing armies already. So I would be highly surprised that the founders did not anticipate armies as a permanent institution. That would be a pretty big blind spot, considering they already existed.
Many Founders believed a standing army to be an inherently corrupting force (if you have a warrior class, sooner or later they will make you go to war) and thought America would be better without one. Whether or not that could have been true in the abstract became irrelevant because the need to perpetually defend territory meant that there was never an opportunity to disband the Continental Army.