As you say, you may not yet be insulin resistant.
Yes, there is a continuum: first, the pancreas produces more insulin than the body needs (due to a high glucose diet OR diseased/inflamed pancreas OR pregnancy OR receiving the BCG (Bacillus Calmette-Guérin) vaccine against tuberculosis repeatedly OR other reasons yet to be discovered).
Next, with the flood of insulin around them, the cells are "beaten into submission" and continue taking in glucose. But then the cells become insensitive or "resistant" to the ever-increasing insulin. The insulin is no longer effective at getting the glucose into the cells. With glucose still floating around in the bloodstream, the pancreas continues to pump out even more insulin to do the job. More insulin, more resistance. Until the pancreas just quits!
All the while the insulin is ramping up, the insulin resistance is becoming greater and greater. More and more glucose is remaining in the bloodstream – this is type II diabetes. The end of the continuum comes when no more insulin is produced – this is type I diabetes.
The exact cause of type 1 diabetes is unknown. In most people with type 1 diabetes, the body's own immune system — which normally fights harmful bacteria and viruses — mistakenly destroys the insulin-producing (islet) cells in the pancreas. Genetics may play a role in this process, and exposure to certain viruses may trigger the disease.
Once the islet cells are destroyed, you'll produce little or no insulin.
In type 1 diabetes, there's no insulin to let glucose into the cells, so sugar builds up in your bloodstream, where it can cause life-threatening complications.
The cause of type 1 diabetes is different from the cause of the more familiar type 2 diabetes. In type 2 diabetes, the islet cells are still functioning, but the body becomes resistant to insulin, or the pancreas doesn't produce enough insulin or both.