My newly-planted clematis took root and was blooming nicely and then suddenly it looked like a pile of cooked vegetables. One of my neighbors said they are sensitive to disease, and this must have been what destroyed it.
How do I keep this from happening again?

@karendauger - There is a disease that clematis get called clematis wilt where the stems suddenly turn black and die. It is suggested that you prune the diseased stems back to the ground. As far as I know there is no way to prevent it. But even if the plant looks dead I would leave it alone. It should regrow new stems from the roots. I've noticed some clematis are more prone to this disease than others.