What does "us or them" mean?

In Pulp Fiction (1994), Pumpkin says to Honey Bunny about difficulties in robbing liquor stores
which owned by foreigners:

Pumpkin: We keep on, one of these g**k fuckers gonna make us kill him.

Honey Bunny: I’m not gonna kill anybody.

Pumpkin: I don’t want to either. But they’ll probably put us in a
situation where it’s us or them.

What does "us or them" mean?

I know the meaning of "us and them" (or) "them and us".