Christy
The cause of endometriosis has a few theories. None completly confirmed. Basically what happens is the endometrium(the inside lining of the uterus) escapes(this is the unanswered ? as to how and why) and settles on what ever organ it chooses. These are called adhesions. These adhesions don't really know that they are not where they are supposed to be and with our cycle they do what they would normally do. They bleed and cramp just like the inside of the uterus does during menstration. Over time they can become very dense and turn into scar tissue. This can cause some people a lot of pain. As far as my research has taken me a D & C is not recommended just because your increasing the risk of more of these cells escaping the uterus and implanting themselves where they shouldn't be. I don't believe there is any prevention. There are many good books out there on women's health. Good luck in your research