Complex sentence: Some Arab historians and Israeli revisionists claim that Israel did expel the Palestinian population, leaving only some 2,000 Arabs behind, whereas traditional historians describe the situation when Arab population was encouraged to leave by their own leaders so they would not disturb in the ongoing conflict.
Split into simpler sentences: Some Arab historians together with the Israeli revisionists claim that Israel did expel the Palestinian population, leaving only some 2,000 Arabs behind. Simultaneously, traditional historians argue that the Arab population was encouraged to leave by their own leaders so they would not disturb in the ongoing conflict.