Deterrence by punishment has served Western countries well. With the exception of a small number of cases, since the end of World War II Western allies – whether acting in informal alliances or as NATO – have been able to stave off armed attacks on their territories and armed forces. The emergence of international terrorist organizations with na-tion-state ambitions began to pose additional challenges on traditional deterrence. Now nation states’ changing behaviour is posing far more fundamental challenges. Countries such as Russia and China could dra-matically destabilise target countries by exclusively using non-military aggression. As the current extent of the activities is already proving, deterrence by military punishment is of limited effect. While societal resilience is not a new concept or practice, today it is severely underutilised. Since hybrid/greyzone/threshold warfare uses seamless aggression, only seamless – combined – deterrence can be effective against it. Working with industry and the wider population, Western governments should enhance societal resilience and use it to strengthen existing deterrence.