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.
Dude could do 40 MPH. So, it could probably prevent human permanent settlement at will.
Which brings me to another thought on that matter. We know the first human beings to permanently settle over a broad area in North America were from Europe ~ the Sa'ami ~ or Clovis Culture people.
So, what is it that they have that bears don't? Well, the Sa'ami have, and had, and may well have had for thousands of years, an item called the SKI.
They can go 60 to 70 MPH themselves.
Those recently revealed rock carvings in the Russian Kola show instructions on how to kill a bear ~ using skis to your advantage.
The article noted the Short Faced bear may well have preyed on the smaller smilodon! But the Sa'ami showed how to trick one to get a new fur coat.