What would movies be about if not for love? Since well before the days of Humphrey Bogart and Ingrid Bergman in “Casablanca,” romance has driven countless classic stories, setting up some of the highest highs in cinematic history to follow. Be it Cary Grant and Grace Kelly seeing stars in “To Catch a Thief” or Meg Ryan and Billy Crystal disturbing diner patrons in “When Harry Met Sally,” the 20th century was chock full of iconic romances that helped humanity fall in love with the movies.