Some of the hallmarks of the 1940s were the presidency of Franklin D. Roosevelt and the impact that the epic movie "Gone With the Wind" had on popular culture. The popular cocktails of that decade are now considered classics for the same reason those aforementioned events made history: Their appeal and influence touched people everywhere, not just the United States.
Frank Meier, who tended bar at the Paris Ritz for 20-plus years, is attributed to inventing the Sidecar. Legend has it that three officers each grabbed a bottle from the bar during a World War I air raid---Cointreau (a name-brand of orange-flavoured liqueur), brandy and lemon juice---and mixed a drink using equal parts of each while waiting for the all clear.
Although popular in the 1940s, the mojito traces its roots to the late 1500s in Havana, Cuba. It was created by a band of pirates to console themselves after they unsuccessful tried to ransack the city for gold. The drink originally contained aguardiente (otherwise known as firewater) along with muddled mint leaves, lime juice and ice. Now, mojitos are mixed with rum instead of aguardiente.
In the 1940s, the Vermouth Cassis was probably popular in the summers since it's a fruity cocktail. The flavour comes from creme de cassis, a very red and sweet liqueur made from black currants. A Vermouth Cassis is made by pouring French vermouth over ice with several dashes of creme de cassis, a twist a lemon and then topping it off with seltzer or cream soda.
When New York City's namesake cocktail was invented in the 1800s, only rye whiskey was used in the recipe. While the drink is now made with maraschino cherries, back in its earliest days it only contained whiskey, vermouth and a dash of bitters that were stirred -- never shaken -- before being poured into a chilled cocktail glass.