Forrest's life through the 1960s, 1970s, and 1980s provides a window to American history at a time when the country was losing its innocence. Again, the book starts off typical enough, with an almost romanticized image of growing up and young adulthood in post-war Alabama. But even that has shades of trouble lurking at its borders. As he continues through his service in war, Forrest sees the horrors of battle up front and personally.
Finally, he loses Jenny, the love of his life, to this terrifying new spectre of AIDS. Remember, Forrest Gump was written in 1986, just as AIDS was entering the public mindset. In having Jenny die from that disease, Groom is saying that we must all pay for the mistakes of our past, and that the terrifying payment of those mistakes comes at a price that is both unknown and terrifying.