Thousands of Iraqi and Kurdish troops, supported by the United States, France, and Britain, are now in the early stages of a massive operation to retake the Iraq's second largest city of Mosul from ISIS militants. Advancing on multiple fronts, the Iraqi assault has so far recaptured numerous outlying villages, but central Mosul still lies ahead. Members of the United Nations and others fear a major crisis may result as hundreds of thousands of civilians are driven from their homes by the war, while ISIS fighters have threatened to fight to the death. In villages already captured, booby traps are being discovered on roadsides, in the remaining buildings, and in networks of tunnels dug beneath them.