Hearts and Minds- Psychological Warfare is an ancient military specialty, but it only get recognized as a separate military career field in the 20th century. Actually, World War II was when Psychological Warfare became a popular item. At first it was the dramatic impact of mass propaganda by the nazis and communists that impressed everyone. It wasn't long before propaganda was being used on the battlefield.
Before that, what we now think of as Psychological Warfare was considered just another form of deception. Deception is largely a mental game. While camouflage, for example, involves a lot of hard work, it's effect is dependent on the enemy believing they are not seeing what is there. Between opposing generals, and to a lesser extent opposing troops, it's a battle of wits. If one general understands the other better, that provides a huge advantage for some effective deception. The classic example is one general knowing what deceptions his opponent is prone to fall for. This is all sort of like a chess game, where this form of deception is widely practiced. It's a mind game, it's Psychological Warfare.
While it's easier to describe deception techniques, all of these depend on how the commanders involved use psychology. The most common cause of a deception failing is that the putative victim simply doesn't fall for it. As a result, Psychological Warfare is considered a riskier operation than simply bombing someone because it is so much more unpredictable. But there have been enough successes in the last sixty years to prompt the American military to invest a lot of money and manpower into Psychological Warfare. This type of military operations rarely wins spectacular victories, but usually provides a lot of little successes. During the 1991 Gulf War, however, Psychological Warfare did strike gold. Once coalition warplanes had isolated Iraqi troops in the desert, they were his with radio, loudspeaker and leaflet appeals to surrender. When the ground forces advanced, 87,000 Iraqi soldiers did surrender, many clutching the surrender leaflets.
Realizing that most people get their information via electronic media (radio, television, Internet). U.S. Psychological Warfare troops increasingly depend on getting to enemy troops via electronic means. Even the poorest nations have lots of radios, and American Psychological Warfare forces have lots of radio broadcasting capability (both with ground and airborne broadcasting equipment.) The airborne equipment is particularly useful, for Psychological Warfare is more effective if it is applied early on.
Once your troops are on the ground, they have to deal with civilians (who may be friendly, or not.) Civil Affairs troops are the folks who deal with any civilians in the combat zone. This has always been a problem, or, as many commanders have noted, a necessary nuisance. Until the 19th century, a general would, at most, assign some officers and troops to go talk to the local civilian leadership to establish some ground rules so that the locals would not interfere with your military operations. This, as any competent general knew, was preferable to just allowing civilians to wander all over the place (often to be abused or looted by the troops, and to sometimes fight back.) But in the last century, dealing with civilians has become a specific military skill. Much of Napoleon's success in the 19th century was due to the attention he paid to civil affairs. During World War II, soldiers with foreign language or government administration skills were collected and used to work with the local civilians and avoid problems.
Current Civil Affairs operations were developed from experience U.S. troops had dealing with occupied Germany and Japan after World War II (1945-55), and "civic action" operations in the Vietnam war (1960-75). Since then, Civil Affairs troops have also been used to administer foreign aid and peacekeeping programs. U.S. Army Special Forces see the Civil Affairs troops as follow up troops for the Special Forces teams that first go in and work out deals with the locals. This enables the more experienced Special Forces to spend more time doing what they do best. The Civil Affairs are trained to continue working with the Special Forces that may have established first contact with the civilian population. More important, the Civil Affairs units know how to work with aid organizations, local and American government officials and many details you have to cope with to keep a population pro-American. The Civil Affairs troops are armed, but their weapons are only for self-defense.
Although the army has long had a monopoly on Civil Affairs troops, the marines have two company sized reserve Civil Affairs units. These troops are to be used to deal with civilians during the unique kinds of operations marines engage in. However, so far, the marine Civil Affairs troops have been doing pretty much the same thing their army counterparts (who belong to SOCOM) do. Eventually, there will be a turf war between the SOCOM (army) and marine Civil Affairs troops on some future combat zone. Taking their lead from the marines, the U.S. Air Force is also creating some reserve Civil Affairs units.
Civil Affairs troops can be decisive. They are proving to be essential in Afghanistan, and any invasion will need lots of well prepared Civil Affairs to handle huge numbers of refugees, prisoners of war and war criminals.