Conventional warfare is a form of warfare conducted by using conventional military weapons and battlefield tactics between two or more states in open confrontation. The forces on each side are well-defined, and fight using weapons that primarily target the opposing army. It is normally fought using conventional weapons, and not with chemical, biological, or nuclear weapons.
The general purpose of conventional warfare is to weaken or destroy the opponent's military force, thereby negating its ability to engage in conventional warfare. In forcing capitulation, however, one or both sides may eventually resort to unconventional warfare tactics.
Formation of the state 
The state was first advocated by Plato, then found more acceptance in the consolidation of power under the Roman Catholic Church. European monarchs then gained power as the Catholic Church was stripped of temporal power and was replaced by the divine right of kings. In 1648, the powers of Europe signed the Treaty of Westphalia which ended the religious violence for purely political governance and outlook, signifying the birth of the modern 'state'.
Within this statist paradigm, only the state and its appointed representatives were allowed to bear arms and enter into war. In fact, war was only understood as a conflict between sovereign states. Kings strengthened this idea and gave it the force of law. Whereas previously any noble could start a war, the monarchs of Europe of necessity consolidated military power in response to the Napoleonic war.
The Clausewitzian paradigm 
Prussia was one country attempting to amass military power. Carl von Clausewitz, one of Prussia's officers, wrote On War, a work rooted solely in the world of the state. All other forms of intrastate conflict, such as rebellion, are not accounted for because in theoretical terms, Clausewitz could not account for warfare before the state. However, near the end of his life, Clausewitz grew increasingly aware of the importance of non-state military actors. This is revealed in his conceptions of "the people in arms" which he noted arose from the same social and political sources as traditional inter-state warfare.
Practices such as raiding or blood feuds were then labeled criminal activities and stripped of legitimacy. This war paradigm reflected the view of most of the modernized world at the beginning of the 21st century, as verified by examination of the conventional armies of the time: large, high maintenance, technologically advanced armies designed to compete against similarly designed forces.
Clausewitz also forwarded the issue of casus belli. While previous wars were fought for social, religious, or even cultural reasons, Clausewitz taught that war is merely "a continuation of politics by other means." It is a rational calculation in which states fight for their interests (whether they are economic, security-related, or otherwise) once normal discourse has broken down.
The majority of modern wars have been conducted using the means of conventional warfare. Confirmed use of biological warfare by a nation state has not occurred since 1945, and chemical warfare has been used only a few times (the latest known confrontation in which it was utilized being the Iran-Iraq War). Nuclear warfare has only occurred once with the United States bombing the Japanese cities of Hiroshima and Nagasaki in August 1945.
The state and Clausewitzian principles peaked in the World Wars of the 20th century, but also laid the groundwork for their dilapidation due to nuclear proliferation and the manifestation of culturally aligned conflict. The nuclear bomb was the result of the state perfecting its quest to overthrow its competitive duplicates. Ironically, this development seems to have pushed conventional conflict waged by the state to the sidelines. Were two conventional armies to fight, the loser would have redress in its nuclear arsenal.
Thus, no two nuclear powers have yet fought a conventional war directly, with the exception of brief skirmishes between for example, China and Russia in the 1969 Sino-Soviet conflict and between India and Pakistan in the 1999 Kargil War.
Conventional warfare, waged by the state, has become something not worthy of a declaration of war. Instead, those capable of fighting underneath the nuclear umbrella (supranational terrorists, corporate mercenaries, ethnic militias, and so on.) have now come to dominate the majority of conflict in the post-modern era. These conflicts cannot be explained under the statist system.
Samuel Huntington has posited that the world in the early 21st century exists as a system of nine distinct "civilizations," instead of many sovereign states. These civilizations are delineated along cultural lines, for example, Western, Islamic, Sinic, Hindu and so on. In this way, cultures that have long been dominated by the West are reasserting themselves and looking to challenge the status quo. Thus, culture has replaced the state as the locus of war. This kind of civilizational war, in our time as in times long past, occurs where these cultures buffet up against one another. Some high-profile examples are the Pakistan/India conflict or the battles in the Sudan. This sort of war has defined the field since World War II.
These cultural forces will not contend with state-based armies in the traditional way. When faced with battalions of tanks, jets, and missiles, the cultural opponent dissolves away into the population. They benefit from the territorially constrained states, being able to move freely from one country to the next, while states must negotiate with other sovereign states. The state's spy networks are also severely limited by cultural factors.
See also 
- Smith, M.L.R. "Guerrillas in the mist: reassessing strategy and low intensity warfare". Review of International Studies. Vol. 29, 19–37. 2003
- "Changing Nature of Warfare". National Intelligence Council. 2004. Retrieved January 30, 2006.
- Stathis Kalyvas (2003). "The Sociology of Civil Wars: Warfare and Armed Groups". Armed Groups Project. Retrieved January 30, 2006.