First, break off your dependence to any nation. Your money is in Swiss or Cayman banks. Your home is a floating island or space station or a cave in the Pakistan-Afghanistan border or somewhere inaccessible. Have multiple homes, and the ability to travel between them quickly. Have no credit cards or accounts that can be shut off by a government. Have an alias. Develop a novel weapon of mass destruction. Build many, secretly. Nukes are too easy, try something biological or else study physics and come up with something new. Amass many of these. Do NOT threaten the world for one million dollars, or a hundred billion, or anything. It fails in movies and will fail in real life. Instead, use the damn things. Target minor population centers, secondary religious centers… basically, spook the planet but leave the biggest targets as threats, and see if you can't get the current nations to go to war with each other. Spare the UN: It is no threat to you (has it ever stopped a dictatorship or war in its entire history?), and will provide a convenient place to address world leaders. Do this all anonymously. Wait. Is the world unstable? Good. Now, come out from the shadows. Show yourself with the new weapons. Threaten the major targets. Did you destroy Osaka? Threaten Tokyo. Did you destroy Medina? Threaten Mecca. Instant two billion people now pliable. Provide an ultimatum for different nations to pledge loyalty, with penalties as deadlines pass. You must make good on every threat: be prepared to eradicate entire nations, staying within borders. You will not be taking over the world as you know it, but the broken one you leave yourself. As nations join you, immediately REPAIR AND REBUILD THEM! With the stick gone, bring out the carrot. Start by being a benevolent leader who lets subject nations keep their laws and their leaders, just being under you. Once they have accepted that for a while, and you've made life better, begin editing their Constitutions or commissioning statues or doing whatever you always wanted, but stay benevolent: you killed many to get where you are, and you will always be an assassination target, so give your new subjects a reason to like and maybe even forgive you.