You don't have to have a family history of diabetes to be at risk for diabetes. It's because most diabetic patients actually suffer from a broader underlying disease process known as Insulin Resistance Syndrome.
Diabetes is just one of the manifestations of Insulin Resistance Syndrome. Other manifestations include high blood pressure, obesity, high triglycerides level, low HDL cholesterol, heart attack and stroke.
If you have a personal or family history of any of these disorders, you are at high risk for diabetes.