The causes of any war are complex. Wars are rarely about just one thing. They can be declared when a state or states act to:
War can also occur internally within a state between organised groups. This is known as civil war.
The Five Precepts are moral guides that all Buddhists try to follow in order to minimise desires and reach enlightenment. The first of these Precepts is to abstain from taking life.
Killing or harming human beings is therefore clearly problematic for Buddhists. Because of this, some Buddhists would not rise to an attack or to any conflict with violence.
In times of war, Buddhists must show compassion and help all living beings. They must abandon any fight that crosses their path.
Even if thieves carve you limb from limb with a double-handed saw, if you make your mind hostile you are not following my teachings.Majjhima-Nikkaya 1:28-20
The Noble Eightfold Path is at the heart of Buddhist teachings. These rules help Buddhists to behave in a peaceful way and to live in harmony with others. For example, they would believe in the importance of right speech and not engage in an argument which might result in a physical fight.
Nevertheless most Buddhist countries have or have had a standing army and have been involved in warfare at one time or another. This is justified either by claiming that military action is an evil necessity, perhaps even to defend the dharma itself; or by giving soldiers a special leave for not observing the precept not to kill.
Ahimsa is the principle of 'non-harm'. Most Buddhists try to practice ahimsa in their everyday lives and believe that it is wrong to show violence at any time. This means that it is possible that a Buddhist may therefore refuse to fight under any circumstances. Some Buddhists are pacifists, even when it comes to self-defence.
Shaolin is a well-known form of martial art which has very strict rules about how violence can be used. The Shaolin teaching forbids the Buddhist monk from ever being the aggressor. This type of martial art is a form of self-defence and uses physical skill to avoid harm.