Why do some people think Islam tells people to kill nonmuslims and start wars?

It is hard to ignore the daily news reports from the middle east where there is a lot of problems. It is the radical Muslims that get all the headlines, and that is unfortunate. The old saying is that "not all muslims are terrorists, but all the terrorists are muslim". Of course that isn't true, but lets face it, the goings-on in that part of the world are very troublesome. I have never heard of western countries using their citizens as human shields, or placing women so low in societal value. These customs are strange to people from other cultures.