"Ice ages don’t end overnight, and after the first flood, the dam reformed"

We are talking about timescales that boggle the mind.

Apart from some pre-historic migrations over land-bridges, all of recorded human history happened within the current inter-glacial - which is just a (rounded) blip compared to the duration of the last glaciation.

See on the left of this

https://en.wikipedia.org/wiki/Last_Glacial_Period#/media/File:Approximate_chronology_of_Heinrich_events_vs_Dansgaard-Oeschger_events_and_Antarctic_Isotope_Maxima.png

PS You might find this interesting https://vimeo.com/294517816