Who Shot First?
The side suffering the most casualties is not necessarily the morally superior side. Nor is the faction who inflicted the first deaths necessarily the "aggressor" in any conventional sense. Many wars are brought on by a reversal of fortune, causing the oppressors to suddenly become the oppressed. Sometimes a persecuted minority arms itself and seizes control, as with the founding of Israel. Other times, the ruling class loses power and finds itself targeted by those it once dominated, as in the Rwandan civil war.
These shifts in power are often driven by larger global forces, such as the end of apartheid and colonialism in Africa, or growing sympathy for the Zionist movement after the exposure of the Nazi genocide campaigns. If nothing else, a shakeup in a society creates chaos and uncertainty, particularly those with something to hide.