What causes diabetes?

I have read so many books and magazine articles on this, yet I still
can not get the matter settled, once and for all. What causes insulin
resistance and diabetes?

Many sources attribute diabetes, at least T2 diabetes, to over eating
and becoming obese. I think this is comparable to looking at the
puddles of water in the street and concluding that those puddles of
water caused it to rain. ;-)

It seems more plausible that something yet unknown or not fully
understood, causes insulin resistance and insulin resistance then
causes high blood glucose and high blood glucose then causes obesity
in some people.

If a person's metabolic processes can not handle the ingested glucose
it seems that this excess blood glucose would be stored as fat while
the muscle cells remained undernourished because of their insulin
resistance. This would stimulate a person's hunger sensation, causing
the person to eat more and more, leading to obesity.

The main question I'm still searching for an answer to is, WHAT CAUSES
INSULIN RESISTANCE in the first place. There may indeed be genetic
factors involved, but what are they?

Thanks for any insights you can provide. Gordon