Reasons for war

• Greed: To gain more land or to control important resources such as oil or gas. e.g. The Nazis invading Poland to gain more land.
• Against using Greed as a reason: "For the love of money is the root of all kinds of evil" - Bible. People who're greedy often stop being a Christian, and end up facing consequences.
• Against using Greed as a reason: "God doesn't like arrogant, boastful people who....order other people to be the same" - Qur'an. God doesn't like people who do not share the blessings he has given them.
• Self-Defence: To defend one’s country against invasion or attack or to protect allies who are under attack e.g. UK threatened by Nazi invasion in WWII.
• Against using Self Defence as a reason: "... those who take up the sword shall punish by the sword" - Bible. Do not use your sword because people who use their sword to kill will face the consequences.
• For using Self Defence as a reason: "Those who have been attacked are permitted to take up arms because they have been wronged." - Qur'an. It's ok to fight back as you are acting in defence.
• Retaliation: To fight against a country that has done something very wrong or to fight against a country that has attacked you. e.g. US invading Afghanistan in retaliation for 9/11.
• Against retaliation as a reason: "If anyone ever slaps you... turn to them the other cheek." - Bible. Do not fight evil people, just turn them the other cheek and forgive them.
• For retaliation as a reason: " If you have to respond to an attack, make your response proportionate, but it is best to stand fast". God has the power to help you as long as you are proportionate with your violence.