The Explosion of the Heinlein World

In this particular Heinlein world there are portals everywhere. And they're constantly opening these new portals onto frontier worlds that can be, uh, habited. You just open up this big thing and then a bunch of settlers march through and colonize the world. Whereas in the expanse, if everybody dies of too many people go in at once or if they exceed the speed or something like that, then you can't just have a free for all.