it's illegal since the Nakba, because starting wars are illegal without UN authorization

and paramilitary forces attacking civilians were illegal in British Palestine

taking private property also

and poisoning wells is also technically not super bueno under a little know statute, the laundry list of deeds for which Hammurabbi will fuck you up personally, but I'm not a legal scholars so maybe it was so legal a mockingbird granted them statehood.

https://en.m.wikipedia.org/wiki/Operation_Cast_Thy_Bread