It's more like part of the random prologue at the begging of a story. If you are going to write more, you should give more detail.
It probably wouldn't be good to write those examples into a prologue.
It would come later on in the first or second chapter, or even later, depending on the format of the story.
What he has up there would work well for an intro, then, if I was the author, I would probably jump back in time to before everything happened, and then start telling the story from there. Showing the character develop and progress until the point in time of the intro.
It would work well as a Chekhov's gun of sorts.
Anyway, if you were going to write the story, you might want to dwell slightly on the consequences of time travel, especially making the character wonder if he would be able to rewind back to the very beginning, so he wouldn't have to deal with any of this.
Opposite that, the alien technology should be considered just that: Alien. Don't try to explain it, don't let the character (and thereby the readers) understand what is going on and how it does such things. Sure, you can have scientists trying to figure out how it was engineered, but trying to explain stuff rationally and scientifically tends to backfire for any author. If it isn't from Earth, don't try to explain how it does what it does. Simple and easy.
As for the snippet up there, I would probably have written something else for the "where the countries were united, against the deadly aliens." part, as it seems somewhat clumpsy and heavy in a sentence like that. It might not be something the readers even need to know at that point in the story, and if it is, there ought to be other ways to communicate this information. Personally, I would opt for the former. If it is a story about one guy with a team, the fact that the world united to fight the aliens might not actually be that great a part of the story anyway, and could easily be explained properly later in the story, without breaking up the story telling too badly, while being kept out of the intro where it doesn't belong.
So, that's my thoughts, at least.
