During the second half of the 20th century, war research saw a new surge of interest, especially as more researchers began to examine the origins and conduct of war. Many philosophers, however, still disagree about how war is connected to morality and justice. Others believe that war is a social disaster.

Some of the theories positing the causes of war focus on human biological factors. These theories have evolved from studies by psychologists and ethologists. The underlying theory is that man is naturally territorial and aggressive. It posits that he has no inherited inhibitions to fight with increasingly lethal weapons.

Other theories point to the effects of social institutions on human behavior. Some philosophers emphasize that war is the continuation of politics by other means. For example, Thomas Hobbes asserted that without external power to impose laws, men are in a state of war. Others, such as Maurice Walsh, argue that the general population is neutral towards war.

Defining war has been a difficult task. The word has been used to mean many things, from the clash of arms to the social disruption it causes. Regardless of the definition used, wars are typically violent, protracted, and widespread. Consequently, students of war must take care when examining definitions.

Some people argue that war is an inevitable outcome of economic competition in a competitive international system. This view is supported by some centrist capitalist world leaders. However, the counter argument is less compelling as the mobility of capital and wealth distributions worldwide increases.

While most scholars are aware of the immense influence that wars have on human life, they generally avoid a sweeping explanation of all wars. This is because they believe that wars are not random accidents. They instead point to a variety of motives that drive wars. These motivations include fear of death, the pursuit of markets for natural resources, and a desire for social stability.

Other theories argue that war is a natural phenomenon, which occurs because man is biologically aggressive and territorial. The emphasis on biological etiology ignores the influence of cultural structures, human will, and intellectual capacity.

A more comprehensive definition of war should encompass more than armed conflict. It should also include the complexity of war in a global society. It should take into account the fact that wars are fought between non-state actors, as well as between states. In addition, it should take into account future wars. It should also take into account the concept of free-market enterprises.

A common definition of war is that it is a conflict between two political communities. This definition may include a state and an opposing group, or a community within a state. It can also include riots, rebellions, and other forms of armed conflict. It can also include the authorization of a sovereign body to declare war.

In addition to the definitions of war, there are a number of sub-disciplines that have tackled the etiology and conduct of war. While some philosophers argue that war does not have a moral component, others point out that wars do require the sacrifice of human life. Moreover, it is important to distinguish between personal violence and collective violence.