What are the laws of war? (link)

[Lord Halifax]

Peace alone is not enough though, one major cause of war is *unjust* peaces.

yes, an unjust peace is usually only stable if the losers are either deported or have their population reduced by assimilation or genocide. If it's a multiethnic state like pre-WW1 Hungary it can lose its offensive capability by being reduced to its core but even then revanchism will still linger. Assimilation is a non-starter in this case which only leave the nasty options if you want to implement a stable unjust peace.