Does religion cause all wars

The short answer is no.

Religion has been used throughout history to generate popular support for a variety of wars, but to say that religion is the cause is a gross simplification. Other things can be used as this "public rallying cry" to bring groups large and small to war. If you look at the battles of the 20th century the most common was nationalism or support of a particular political ideology. I would argue that most (or all) wars are caused by leaders trying to increase their power / wealth / position / prestige etc...

To common examples in European history which are advanced are the reformation and the crusades. A careful look at these events reveal other forces which may have been driving decisions at the leaders level.

Before the reformation the Catholic Church was one of the wealthiest entities in all of Europe. If the king told peasants "Go fight for me so i can take the land, buildings, gold, treasure of the catholic church for the Crown." he would likely have a difficult sale. "The Pope is trying to corrupt your soul and if we don't stop the church...bla bla bla" is more effective.

The leaders of the early crusades were younger sons of nobles unable to inherit lands in Europe. Again , telling the peasants "Lets go to the Holy Land where you will fight to carve out lands for me and my noble buddies" is less than appetizing. If we say "Come Christian warriors, we must smite the infidel and defend the holy land. If you fight in the crusade your Soul will be saved." You can raise an army and go fight your war.

You can say that religion has been used as a tool to bring the public to war but to say it is the cause of war is wrong. Rarely in history has a war been fought for the reasons given to the masses.