Diabetes occurs for a number of reasons, but the ultimate cause of the high blood sugar that characterizes the dis-order is either deficiency of the hormone insulin or a combination of insulin deficiency and resistance of the body tissues to its actions. In response to food intake, insulin is released by specialized cells in the pancreas and is necessary for adequate amounts of glucose and other nutrients from food to be absorbed into certain tissues of the body. When insulin is lacking or the body resists its actions, the level of glucose in the blood becomes excessively high and diabetes is diagnosed.
The difference in the balance between the two characterizes the two major forms of diabetes—type 1 and type 2 Whatever the form of diabetes, its basis is to some extent hereditary and to some extent environmental. The hereditary contribution is more or less constant throughout recent human evolution. It is the environmental component that has changed markedly over the last 100 years, leading to the dramatic rise in the frequency of diabetes in almost all societies.
You developed diabetes because either you are strongly pre-disposed due to hereditary reasons or because there are factors in your lifestyle and environment (such as gaining weight, getting insufficient exercise, taking certain medications) that increase the likelihood of diabetes or, as is usually the case, a combination of both. This is not all bad, because the environment and lifestyle can often be changed, with dramatic improvement in the severity of the diabetes.