What makes a war just?

There have been many wars fought throughout history. Each of these wars could be found to be either just or unjust. The way to determine this is by a set of guidelines that have been made by historians and philosophers over the years. This set of rules is called the jus ad bellum or right to war. The six guidelines included in this set are as follows: legitimate authority, just cause, right intention, last resort, reasonable chance of success, and an end goal of superior peace. I believe that, according to the jus ad bellum, the declaration of the First Crusade by Pope Urban II was just.
The first of the rules that must be examined is legitimate authority. This is determined by the cultural context of the war. Legitimate authority can change because different cultures believe in their own authority. For example, throughout the Bible the only legitimate authority was God and in America the only legitimate authority is the Congress, by the request of the President. In the time of the Crusades, there were two authorities that could declare a war legitimately, the king and the pope. The pope had the authority when it was not a state war but a religious war. The First Crusade was declared by Pope Urban II (Malmesbury’s Chronicle p. 359-363). This declaration makes the First Crusade just by legitimate authority.
The next of the guidelines must be looked at through historical context as well. This guideline is just cause. A just cause for going to war is defense against a tyrant or an aggressor. This is the cause of many wars and should always be considered a just cause. Many times God told the Israelites to go to war because they were being oppressed. The cause of the First Crusade was to defend Christians against an aggressor, the Turks. The Turks had been forcing the Christians, who were on pilgrimages to Jerusalem, a fee to go to the city. Along with this, they were attacking the Christians, which caused them to live in danger and fear. (Malmesbury p. 359-363. This