Is there an external good and evil?

Why do people believe there is some great external good and  evil? Since I am not educated like most of the writers I read, my answers to questions like this tend to have holes in them. Unlike those educated in the fields involved with the above question I try to find simple explanations. I also think to many people want to use evidence to much. Evidence only works if the person you are talking to wants the evidence to work. To change someones mind you need more then just evidence. Most people who believe in an external good and evil does so from what they believe and claim their evidence is stuff like natural disasters and when things go good for them.

The way I see it, to believe in an external good and evil, you must also believe we don't really control any part of our lives. Wehn you believe that these two forces are fighting over you everlasting soul doesn't that mean that every thing you think has to come from them. I know chrisitans will claim there is free will. Free will doesn't really fit with there beginning some great plan by an external good. I have been told that we have a choose but that how we will chose is already known. The way I see this statement is I have only one choose even though there might be several thousand to make.