Amos,
"What strategic and tactical programs should a Deparmtent of Peace pursue in order to address and defuse the root causes of violence among people??"

I suggest a start could be made by an earnest attempt to address grievances.
Ammong other things, the Arabs are pissed off because they were promised an independent homeland if they would just help beat the Turks, and then had to watch as their territory was divided up by the superpowers, leaving them next to nothing.
This is just an example. There are many peoples with many grievances which need to be addressed, and I emphasise EARNESTLY.

John