Anything that damages the language centers of the brain can cause aphasia, including:
Stroke, which occurs when a clot blocks a blood vessel in the brain, which prevents blood supply to areas of the brain supplied by that vessel.
Traumatic brain injury (also known as TBI), an event where the brain is hit and damaged by trauma, or by disease, such as brain tumor or encephalitis.
Hemorrhage or aneurysm, when a blood vessel ruptures in the brain. Blood is “poisonous” to the brain, so if any parts of the brain are exposed to blood during a hemorrhage, they will be damaged.