Many people will do things during a war that they would never do before. Crimes against humanity and crimes of opportunity often result. For example, people will do things because they are only following orders. Some people will do things just because they can get away with it in the chaos of war. Some people also do things out of desperation, such as looting because there is no food.
War, by its very definition, involves the break down of the basic infrastructure of society, such as law and order. This results in a massive freedom to commit crimes without consequences, thus leading to a massive increase in many different crimes. Of course, without any police force, the temptation to engage in looting and robbery among other, much more serious crimes, must be very great.
It is often difficult to assess the criminal aspects of war, since so many of the things that happen in war--killing, looting, etc.--are illegal in civilian life and peacetime. It's why many of the "rules" of war seem so absurd on the surface. I can shoot the enemy until he drops his weapon and puts his hands up. I can only use certain kinds of bullets. I can use high explosives to kill people but not poison gas. This is why the prosecution of people for war crimes is always carried out by the victorious side, and those prosecuted are on the defeated side. In other words, power enforces the law selectively, refusing to apply it in most cases to its own examples of war crimes.
I think the post on war-profiteering is particularly interesting because in previous wars, profiteering was considered a completely normal and accepted part of the conflict, in certain arenas. Governments issued warrants to private citizens to intercept shipping and then rewarded them for taking these enemy ships or "prizes." This is a different approach but in some ways mirrors the way the government looks the other way to encourage behaviors that benefit it in the long run.
If you read Studs Terkel's book The Good War, the people he interviews make it quite clear that industry folks knew they would profit big time from war production, the laws were window dressing to make people feel better about it.
As mentioned in the above posts, crimes in war-torn states are not usually planned. They are committed out of necessity or out of opportunity. Children who are orphaned steal food, items to sell, or pick pockets to survive and/or provide for siblings. People rob, rape, steal because they think they won't get caught and/or won't have any consequences.
As mentioned in the previous posts most of the crimes that result from war are crimes of opportunity, usually unrelated to the actual conflict. Rape and looting result because of the precarious conditions that civilians in a war zone live in. The same could be said for racketeering (money for "protection" from the dangers of the area). Indeed war profiteering is the best example of this as most war profiteers don't care about the causes of the war or which side they will be benefitting, in fact often taking advantage of both sides. It is a crime of opportunity. They can make money so they take it.
This answer was not covered by previous responses. The crime of War profiteering was not mentioned as it is somthing of an invisible crime. It is not noticed unless one is caught and accused of it. Individuals and corporations are able to charge a higher price for goods and services rendered because they are needed for the war efforts.
Profiteer: Make excessive profits: to make excessive profits by charging high prices for scarce, necessary, or rationed goods. n (plural prof·it·eers) somebody making excessive profits: somebody who makes excessive profits by charging high prices for scarce, necessary, or rationed goods. -prof·it·eer·ing, n (Encarta ® World English Dictionary).
Below is only one example noted in recent times:
Knight Ridders' Seth Bornstein reports on May 21, 2004, that "Empty flatbed trucks crisscrossed Iraq more than 100 times as their drivers and the soldiers who guarded them dodged bullets, bricks and homemade bombs.
"Twelve current and former truckers who regularly made the 300-mile re-supply run from Camp Cedar in southern Iraq to Camp Anaconda near Baghdad told Knight Ridder that they risked their lives driving empty trucks while their employer, a subsidiary of Halliburton Inc., billed the government for hauling what they derisively called 'sailboat fuel.'
During World War II, profiteers were checked and laws were made that attempted to curtail war profiteering by pursuing Anti-Trust laws that were already on the books. (http://news.google.com/newspapers?id=SE81AAAAIBAJ&sjid=a3EFAAAAIBAJ&pg=1582,4982793&hl=en). However, War profiteering has been a problem in every war the United States has ever been involved in all the way back to the Revolutionary War.
While every method is taken to bring to justice those men whose principles and practices have been hostile to the present revolution, it is to be lamented that the conduct of another class, equally criminal, and if possible more mischievous, has hitherto passed with impunity, and almost without notice. I mean that tribe who, taking advantage of the times, have carried the spirit of monopoly and extortion to an excess, which scarcely admits of a parallel. Emboldened by the success of progressive impositions, it has extended to all the necessaries of life. The exorbitant price of every article, and the depreciation upon our currency, are evils derived essentially from this source. When avarice takes the lead in a state, it is commonly the forerunner of its fall. How shocking is it to discover among ourselves, even at this early period, the strongest symptoms of this fatal disease.--Alexander Hamilton 1778
War profiteering is a crime because it undermines the military's ability to complete the mission and places undue burdens on the tax payers who are funding the war.
The timeline link will allow you to click through various years and see links to primary source material regarding this crime.
In wars crimes against civilians are very common. Apart from the fact that they are displaced due to armies fighting there, face a lot of economic damage and many die due to collateral damage, in many instances civilians are intentionally targeted by the leaders of the enemy nations.
Thousands of civilians are captured and kept in camps under the most inhumane conditions. Their labor is used to help produce products for the use of the enemy nations. The torture of civilians is also used to send across a signal to the army they are fighting against of their power and to make them lay down arms. The torture of civilians is also a way to force them to take up arms against their own nations. They are also used as a means to restrict the armies of the nation they are fighting against as it would be wary of injuring its own people.
Such atrocities during wars are referred as war crimes, and the United Nations has made the punishment of leaders involved in these actions something that it takes very seriously.
Many kinds of crime tend to result from war, especially in the sorts of relatively informal, guerrilla conflicts that now occur within countries (as opposed to international wars) in many parts of the world.
For example, one of the major "new" crimes associated with war is rape. A recent article in the Economist (link below) documented how widely rape is now used as a weapon of war and/or as a result of the chaos of war.
A second kind of crime related to war is looting. This is in no way new. War, once again, brings chaos. Chaos means that law and order breaks down. It also means that people can be unable to buy the things they would normally need. Between the people in need and the opportunists, many people loot homes and businesses in war time.