you don't need a massive amount of brute force to take over the world. That's so primitive and silly. I like to look back at classic super-villains and see how they almost accomplished such a feat as ruling over an area or the world itself.
An example I like to use is Shishio from RuroKen. He planned to plunge Japan back into Anarchy and chaos after the peace had started post Tokugawa wars. He wanted to rise up from that Anarchy as Japan's new leader. So, it's simple. Plunge the world into total chaos and anarchy. There are MANY ways to do this ranging from nukes in every major world city (not hitting them, just hidden in them) to a global-scale EMP. Without our tech, people will likely panic. Maybe unleash a new disease or revive an old one that we've forgotten about. From that anarchy, rise up and take the reigns of leadership. It's pretty simple and way more fun than financial take over or simply amassing a large army.
An example I like to use is Shishio from RuroKen. He planned to plunge Japan back into Anarchy and chaos after the peace had started post Tokugawa wars. He wanted to rise up from that Anarchy as Japan's new leader. So, it's simple. Plunge the world into total chaos and anarchy. There are MANY ways to do this ranging from nukes in every major world city (not hitting them, just hidden in them) to a global-scale EMP. Without our tech, people will likely panic. Maybe unleash a new disease or revive an old one that we've forgotten about. From that anarchy, rise up and take the reigns of leadership. It's pretty simple and way more fun than financial take over or simply amassing a large army.