Complex sentence: The film begins with the character George Herbert, who explains that despite years of searching for extraterrestrial life, mankind could never have predicted the invasion, and that the aliens fed on human blood, which infected them, wiping the invaders out.
Split into simpler sentences: The film begins with George Herbert, who explains that despite years of searching for extraterrestrial life, mankind could never have predicted the invasion. He tells us that the aliens fed on human blood which infected them, wiping the invaders out.