**Core Concept**
Addison's disease is a rare endocrine disorder characterized by the insufficient production of cortisol and, often, aldosterone hormones by the adrenal glands. This condition can be caused by various factors, including autoimmune destruction of the adrenal cortex, infections, and genetic disorders.

**Why the Correct Answer is Right**
The most common cause of Addison's disease is autoimmune adrenalitis, where the immune system mistakenly attacks and destroys the adrenal cortex. This process leads to the destruction of the cells responsible for producing cortisol and aldosterone, resulting in the characteristic symptoms of the disease. The autoimmune destruction of the adrenal cortex can be triggered by genetic predisposition and other environmental factors.

**Why Each Wrong Option is Incorrect**
**Option A:** Tuberculosis (TB) is a historic cause of Addison's disease, but it is now a rare cause in developed countries. While TB can still cause adrenal insufficiency, it is not the most common cause.
**Option B:** Genetic disorders, such as congenital adrenal hyperplasia, can cause adrenal insufficiency, but they are not the most common cause of Addison's disease in adults.
**Option C:** Adrenal hemorrhage is a rare cause of acute adrenal insufficiency, but it is not the most common cause of Addison's disease.

**Clinical Pearl / High-Yield Fact**
Autoimmune adrenalitis is the most common cause of Addison's disease, and it often coexists with other autoimmune disorders, such as autoimmune thyroiditis and type 1 diabetes.

**Correct Answer: C. Tuberculosis (TB) is a historic cause of Addison's disease, but it is now a rare cause in developed countries. While TB can still cause adrenal insufficiency, it is not the most common cause.**