War in Islam is a high calling but he has to have a justifiable means not just end. It also has to make things better not worse, if it makes things worse then its left.
There are two kind of struggle spiritual and physical, the spiritual one is higher.
the King "Herucl", sent out an army of 100,000 men and ordered them to go to "Medina" in what we call today Saudi Arabia to destroy Islam once and for all.
The Muslims were not stable yet at that time, and they only sent out an army of 3,000 men at that time to drive the Christian Romans away from Medina. The battle was named "The battle of Mo'ta" and it took place in Mo'ta, Jordan today.
The Muslims' plan was to meet the Christian Romans far away from Madina, and to have them stray away from Madina. The army of 3,000 men was successful enough to fight the Christian Romans for few days and then to pull away from the battle and headed South of Jordan. The Romans strayed away from Medina and the small army of the Muslims was able to run away through the mountains. More than half of the 3,000 Muslims however were killed in this operation.
The point is that Islam didn't spread by sword with much choice. The wars were imposed upon the Muslims. The Muslims didn't ask for those wars.