Yesterday another post (sorry that I can't remember by whom) quoted Jenny Ruhl who says that diabetes is a symptom, not a cause. It was a welcome reminder for me.
Basically, type 1s don't produce insulin. Type 2 don't produce enough. That's very simplified.
But what causes the insulin deficiency? Fatty liver? Large body mass? Immune problems following a virus? Toxic chemical exposure? Medical drugs (also toxic)? Complication from another problem or disease? Trauma (physical or emotional)? Grief? Organ deterioration through age? Diet? Lifestyle? Genetics?