What exactly does diabetes actually do, how is it caused, and what leads to it?

Diabetes = HighSugar: When healthy, we control blood glucose with great precision. The mechanisms are complex, only partially understood & involve multiple hormones: insulin, amylin, glucagon, adrenalin, noradrenalin, growth hormone, resistin, etc. If we no longer do a good job & allow glucose to go high enough, this failure, after bad enough, is called diabetes mellitus, type 1 or type 2. Dietary sugar aggravates.