Peace Believer,
A few points that needs to be clarified.
1) Muhammad pbuh sent envoys to states nearby and far away, to call people to the way of God. The envoys were killed or humiliated in most cases.
2) When dispersed Arab tribes united under Islam. Byzantium and Sasanid empires were concerned of this and sought to take measures. It was their hostility which led to the wars.
3) You say "Islam went seriously against teachings of Jesus." I assume you mean "since Islam accepts Jesus pbuh as a former prophet, it should not bring anything against his teachings."
[That is interesting to say, because you should first of all ask whether Christians ever kept in line with teachings of Jesus pbuh.]
Ok, dont look after Jesus pbuh but look back to the other prophets before him. If Muhammad did something contrary to his teachings, so did Solomon, David, Moses. Solomon and David were rulers-prophets. Moses urged Jews to fight at several times after the exodus. By your thinking we can say Jesus pbuh was going against teachings of Moses pbuh.
Muhammad pbuh did nothing but God's commands. There may be differences in character of the Message from prophet to prophet. Jesus pbuh came to give tidings of Muhammad pbuh. The message he brought was excelled by Muhammad pbuh. Jesus came as a relieve to people under oppression of pagan Roman Empire. Muhammad pbuh cleaned the last remmants of pagan Roman empire in the region (although they seemed later to accept Christianity in surface). Mahmad II cracked walls of Constaninople. And time will come where last castle of pagan Rome will fall. (This is not hope, or wishful thinking. It is prophecy. Let's see whether it will come true)
4) Paul is the primary corrupter of the message. He is not a great missionary.