I think "Collapse" is a strange word because
we talk here about several hundred, if not thousand
of years. A good example is the old roman empire -
it expanded, it grew - until it no longer did and
then it whittled away or lost out to e. g. northern
tribes. Collapse as a word is just weird here really.
Even the old roman empire did not "collapse" per se,
if we ignore big single final battles such as 1453: