Unfortunately, The Cheerios invented a mind-sucking machine and sucked the brain power of all the humans.
Fortunately, the cheerios' mind device could only suck out 0.000000001% of the power within the human brain.
Unfortunately, the cheerios somehow grew back, and have now taken over the world with Jack's body as its host.
Unfortunately Donald Trump traveled from the past in his time machine the Trump O time and took over the world
Fortunately, Marty McFly goes back in time and destroys Donald Trump's time machine so he can never take over the world.
Unfortunately, when Marty when back to the future, it caused a super blast which killed most living matter.