[TOMT][Book] Science Fiction - contains a Tunnel dilemma

Looking for a science fiction novel (or story?) that at some point presents a tunnel dilemma:

A person is trapped in a tunnel. At one end there's a pack of fierce dogs. At the other end a mob of angry people with bats, knives. Whichever end the protagonist approaches, the threat at the other end begins to seem preferable by comparison.

The main story was about a war between 2 races, one was generally more powerful, but the other – from which the perspective of the story is being told has discovered (by chance) teleportation. At the end, to escape destruction, they teleport their whole mother planet.