Some aliens have so much unexplained anger. The very sight of another intelligent species sets them off and all the humans can do is fight.
It possibly began with The War of the Worlds, the classic HG Wells that depicts the invasion of Earth by martians. Written in 1898? it still conveys the paranoia of the period, where other countries were as mysterious as beings from another planet. (free ebook)
Joe Haldeman's Forever War.
Robert Heinlein's Starship Troopers.