(although based on numerous sightings from the 1790s to the present, there may be relict populations of the lions still around)
are you talking about mountain lions or the lions extincted by the events of the younger dryas.
(I’ve never read reports of any lions but mountain lions in the USA. as to other big cats, I’ve seen pictures of jaguars north of the border.)
The main impediment to human settlement that I’ve seen claimed from time to time is the short-faced bear; the sabretooth cat might have been a bit troublesome too. OTOH, we know human toolmaking and weaponmaking is a couple million years old, too. Weird coincidence.