This grappling with the problem of definition will help you compile an annotated list of successes, and you can then proceed to explain them, tracing their origins and pinpointing how and why they occurred. Is there any specific event that marks his achievement of power?
Do not ignore this advice.
You are required to propose a thesis about certain historical events, figures, groups, etc. It also fatuously presupposes that historians are infallible and omniscient gods. Middle Paragraphs Philip Larkin once said that the modern novel consists of a beginning, a muddle and an end.
Get into the habit of criticising your own first drafts, and never be satisfied with second-best efforts. The paragraph structure recommended above is just a guide, nothing more, and you can write a fine essay using a very different arrangement of material.
What follows, therefore, skips philosophical issues and instead offers practical advice on how to write an essay that will get top marks. The introduction — the introduction is where you start your writing.