The point of a secret world government is the real leaders are immune to personal consequences. Why would they ever give that up? Let's say you want to rebuild a city with modern infrastructure... how are you going to make a million people leave their homes? Thats why "world peace" will never happen -- war is too useful a tool. The only reason to do an apocalyptic alien invasion is to utterly destroy the old world. Then, they can blame it on "the aliens". And if they do an open world government, the real rulers will be still be hidden, because thats optimal.