Question

What is the difference between a permanent peace and one built "upon quicksand"

Answer 1

A permanent peace be ever-lasting and one built "upon quicksand" will eventually sink into the sand or as realistically be gone (if this is wrong i apologize)

Answer 2

Quicksand is a type of loose sand or soil that cannot support weight. The expression "upon quicksand" plays on the characteristic of quicksand to "swallow" things that fall on it. Because of this quality, quicksand is a terrible foundation upon which to build something. Therefore, the difference between a permanent peace and one built "upon quicksand" is that the former is likely to be long-lasting, while the latter has weak foundations and is unlikely to last very long.