That's because our invading forces were more advanced than those overthrown. Once things started to equal out we lost the control. Israel is currently the advanced military force who is choosing, and has admitted it, to overthrow any hope the Palestinians have of a country of their own.
As with the French resistance which Britain supported during the war, murder of opposite supporters was part of the course by any means possible, even if that involved the death of civilians, as long as it worked towards the end game of getting the invading force out.