Dear Dona —

None of these examples pertain to violating peace, at least in the sense of war. They are all mandates of capital punishment for individual offenses. In fact, they are intended to keep peace by purging evil, which brings war and destruction, from the midst of the nation. 

In the first case, God did not give the order; the nation decided themselves to do it.

In the second and third cases, grave crimes were involved, and God commanded death to purge the evil from their midst, evil that he knew would ultimately bring negative consequences on society.

There is a reason a policeman is also called a "peace officer", because when crimes go unpunished, it disturbs the peace of the community. 

True peace is found in obeying God's commandments, since he knows how we are made and what brings us authentic peace. We are fallen; we seek good things by evil means and bring evil and lack of peace to ourselves. We need the light of God's law to show us the way to true peace, and by imposing capital punishment for certain sins, God shows us how serious these matters are and motivates us to obey.

Eric