Diabetes mellitus without complication, primarily includes type 1 and type 2 diabetes, arises from a combination of genetic, environmental, and lifestyle factors. In type 1 diabetes, the immune system mistakenly attacks insulin-producing beta cells in the pancreas, often leading to a complete lack of insulin. Type 2 diabetes, more common, is associated with insulin resistance, where the body's cells do not respond effectively to insulin, often accompanied by obesity, physical inactivity, and a family history of diabetes.