1. Rough childhood driving him to resort to narcissism to escape depression.
2. Narcissism driving him to blame others for all problems.
3. Methamphetamine and testosterone kicking the regular madness to the next level.

www.quora.com/…/Harri-K-Hiltunen

the infantile narcissism will be preserved as a kind of psychological fortress to protect the child against the vicissitudes of its intolerable life. Thus children may become evil in order to defend themselves against the onslaughts of parents who are evil.
… it is out of their failure to put themselves on trial that their evil arises. When they are in conflict with the world they will invariably perceive the conflict as the world’s fault.

psychiatrictimes.com/…/methamphetamine-dictatorsh…

Morell’s notes reveal that he put Hitler on a regimen of Vitamultin – a preparation containing glucose, vitamins, and sometimes the methamphetamine Pervitin – and prescribed dietary restrictions, bloodletting, leeching, enemas, and the morphine derivative Eukodal to relieve the GI symptoms. Sedatives (for sleep) and testosterone (for sexual potency) were also among the considerable number of drugs (over 40 different kinds) Hitler took over the course of his adult life.

Does methamphetamine use increase violent behaviour? Evidence from a prospective longitudinal study

Conclusions: There is a dose-related increase in violent behaviour during periods of methamphetamine use that is largely independent of the violence risk associated with psychotic symptoms.