Emil kraepelin gave the label "dementia praecox" to the disorder now known as schizophrenia because he believed that the disorder resulted from:

Premature deterioration of the brain.

Explanation:

In 1883, Emil Kraepelin referred schizophrenia as a "dementia praecox" as a way to differentiate it from late dementia, which relates to Alzheimer. Ten years later, in 1893, he described this clinical picture as a series of medical conditions which share peculiar destruction of a mental personality's inner connections.