In 1955 Robert Oppenheimer, the physicist who led the project that developed the first atomic bomb, addressed the American Psychological Association. He warned that both physics and psychology could endanger humanity but that psychology "opens up the most terrifying prospects of controlling what people do and how they think". Despite Oppenheimer's warning, the idea that you could change human behaviour to win a war, rather than winning a war to change human behaviour, languished as an also-ran in the cold war arms race. But as information technology has begun to globalise and behavioural science has entered the mainstream, there is an increasing move to put psychology at the centre of military operations.

Techniques such as deception and propaganda have been the mainstay of warfare for thousands of years, but there is a growing belief that the modern world has changed so fundamentally that war itself needs to be refigured. Confrontations between standing armies of large nation states are becoming rare while conflicts with guerrilla or terrorist groups, barely distinguishable from the local population, are increasingly common. In other words, overwhelming firepower no longer guarantees victory.

As a result, dissuading people from taking up arms is as much of a military objective as killing the people who actually engage your troops. To the insurgent, influence is crucial, owing to the impossibility of winning the conflict through the force of arms. Violence, then, becomes not an act of war, but an illustration of resistance. For both sides, showing successful attacks on the opposition or highlighting the abuses of occupying forces is essential to forcing a withdrawal through undermining domestic support or fomenting international unpopularity.

The latest report on global strategic trends from the Ministry of Defence calls this "armed propaganda", highlighting the fact that attacks may be staged as much for their value on YouTube as their physical effect in weakening the enemy. From this point of view, all wars are media wars and, with this in mind, the MoD predicts that "kinetic" force will become less important as social influence becomes increasingly significant in defending British interests.

Social influence has traditionally been conceptualised as winning hearts and minds, but many military thinkers are now focused on a new approach informed by the behavioural sciences. A milestone in this approach has been the book Behavioural Conflict by Major General Andrew Mackay and Commander Steve Tatham, who co-ordinated influence-informed British military operations in Iraq and Afghanistan. The book has become a core text for a new generation of officers and argues that changing behaviour – not beliefs or perceptions – is the key to military influence. This is an alternative to the propaganda or public relations model that says that getting the target audience to share your beliefs and understand key information is central, despite well-established research showing that beliefs and attitudes are relatively poor predictors of behaviour.

Mackay and Tatham argue that researching what motivates people within specific groups and deploying informed, testable interventions on the ground will be central to managing modern conflict. The incorporation of behavioural economics, anthropology, psychology and "boots on the ground" research methods to test for genuine behavioural change mark it out from previous approaches which are largely taken from advertising.

To take the example of the war in Afghanistan, a great deal of effort has been spent on encouraging the population to support the introduction of democracy, when the extent to which ideology affects co-operation either with the occupiers or insurgents varies greatly depending on local context. The need to put food on the table, fear of armed groups, resentment of foreign imposition and the solidarity of social ties may all be more important in motivating behaviour than a belief in a certain political order. With this in mind, "target audience analysis" to understand the local population's motivations for collaboration, say, could lead to a tested programme of financial support. This could target reasons for supporting the insurgents, perhaps poverty, with a reduction in insurgent attacks being a measurable outcome. In this view of conflict, the military are, in part, social engineers prepared to work in the most dangerous places on Earth.

But attempts at influence are not just focused on the theatre of war. In a 2011 article, psychologist Sarah King tracked the extent of the US military's work in the "global information environment" and noted how "information-operations" thinking is becoming pervasive across military campaigning. Defined as attempts to "influence, disrupt, corrupt or usurp adversarial human and automated decision making" that can stretch into the civilian world, information operations includes behavioural change programmes, cyber warfare, essentially hostile computer hacking, and "strategic communications", a form of impression management that involves attempts to steer the global news agenda to favour the military's objectives. This could range from providing new organisations with vetted video footage to having a cadre of clandestine internet users who push key talking points in the comment sections of the internet.

The fact that a behavioural change programme, a public relations campaign, computer hacking and an air strike to take out an enemy radio station would all be considered legitimate information operations is perhaps the best reflection of how warfare has changed in the 21st century. Critics argue that the whole process is anti-democratic, but it could also be argued that it is simply a reflection of how belligerent forces are having to adapt to an age where, for the first time in history, information is sent across the globe in seconds and public opinion is the final arbiter of success.