Rick Hillier, former Canadian Chief of the Defence Staff, argued that "I know that NATO is a defensive organization but you don't start defence at your front door," and argued that if a no-fly zone had been imposed prior to the invasion "Putin might have had second thoughts before he launched."[17] Former American Ambassador to NATO Kurt Volker called for a limited no-fly zone to established over certain areas of Ukraine "to create a clear space where there are no attacks against civilians to allow humanitarian assistance to flow and civilians to leave safely."[18]