If i was going to conquer the world? I would first start a few colony's on mars, and wait till the population reaches 50 million. Then, i'll have enough dedicated henchman to build my doomsday device which i have designed (seriously, i've got it drawn out with about ten pages of notes and diagrams, locked up in a safe) and i can threaten the world with either a small amount of destruction (an important building, e.g Buckingham Palace) or the destruction of all life on Earth. If they don't obey my commands, then i destroy all life and carry on humanity and civilisation on Mars. If they do obey my demands, then i make sure that i unite the entire world, and make humanity a space faring civilisation, exploring the stars, setting up home on new planets, while making sure everyone lives peaceful happy lives, and anyone who speaks out against me or has a different opinion to me is dragged out of their house at night into the back of a black car and never seen again.