He’s also pathetically insecure, and history has traditionally looked back fondly at wartime leaders like Churchill and the like. He’s hoping for that

A key thing to note is that it’s normally defensive leaders that are looked back on fondly. Attacking another nation usually doesn’t give this boost, or at least not as significantly. Frequently it’s negative in fact.

He’s too stupid to understand this though, if this is his reason. I don’t think it is though. At best, it’s a distraction. At worst, and more likely, it’s an excuse to implement policies that expand his powers, and maybe to prevent elections from taking place.