Before attempting to justify warfare, we first have to assess the term justice and its significance in warfare. Justice is crucial in this discussion because it has taken over from religion as a basis for moral judgement when fighting a war. Historically, medieval Christian ethics were the justifications for warfare, as was apparent throughout the Crusades. Justice became the highest moral value after the conflict between Christ as a pacifist and the fight to spread Christianity. From this stemmed the principles of the just war tradition. There are seven principles of just war tradition and they are referred to as "ius ad bellum," which translates from Latin to read 'justice of going to war.' This tradition of restrictions has influenced modern declarations and treaties concerning the conduct of war.
The word war can have many different meanings: nuclear wars; conventional wars; world wars; civil wars; religious wars; tribal wars; revolutionary wars; trade wars and others.
Even if we consider the 'simple' form of a conventional war between two countries, there are certain moral issues that have to be addressed. Was the government justified in committing the country to war? Should the use of nuclear, chemical or biological weapons be undertaken? Can the military authorities use methods of torture on its prisoners?
There are as many different degrees of pacifism as there is patriotism but no recognizable version allows killing even as a defensive act. Absolute pacifists agree with the title and say that it is never right to kill another person, however evil the consequences of not doing so. This is due to their key principle being the sanctity of life.
Many people take the view that it is always wrong for a government to start a war, but always legitimate for a government to meet external aggression with force.