The recent book I read "Hail Mary" offered a nice example of my premise. Space microbes were eating our Sun, at a rate that was increasing and it meant the end of humanity in about 40 years. It's a weird concept, but it's fiction. In the book, somehow unrevealed, complete power over every country was given to a single woman who ran everything to try and come up with a fix. There were folks who disbelieved this of course, she handled them rather abruptly.
I don't think this could happen, the world unity under one person part, no matter the threat.