Sugar is a problem with glucose metabolism. It is essentially a glucose intolerance. This does not mean that diabetes was caused by sugar. Chronic hypoglycemia or hyperglycemia may play a role it's development but it is just one factor. As I said in the comments off the original post, it is likely caused by PUFAs but it may develop due to general food toxins (this can include excess fructose), environmental toxins, vitamin and mineral deficiencies, and an inability to detox. Genetics can make some one more susceptible to developing diabetes.
Once the disease has developed, it is characterized by high blood glucose, insulin resistance and excess of insulin in the blood stream (type 2). Western medicine misleading calls this 'relative insulin deficiency' meaning that diabetics already have high insulin but it needs to be higher in order to get glucose into cells. This makes diabetic's glucose intolerant without hormonal intervention which leads to slew of other problems.
Just as gluten likely does not cause gluten intolerance (a leaky gut typically does), glucose does not cause diabetes. The question is about causation not about 'once I have the disease.' Causation is a more complicated story. In diabetes, its it's basically a story about metabolism insufficiencies leading to hormonal insufficiencies leading to glucose intolerance, but this story could be told many different ways.