After Star Wars was an overwhelming success in the summer of 1977, there was obvious pressure for a sequel. Thankfully, George Lucas had a vision for the complete saga of Luke Skywalker ready to go and he didn't kill Darth Vader at the end of Star Wars. 20th Century Fox probably assumed that Lucas would present them with another feel-good, swashbuckling Western in Space. But that was not what Lucas planned at all. For the first time, a sequel would not just be another adventure with loveable characters, but a film moving the story forward and even leaving a cliffhanger.

Star Wars was always envisioned as a series of episodes, a tribute to the old serials that dominated cinemas in the 1940s and 1950s. These always ended with cliffhangers until one story arc was finished. Lucas completed his first arc in Star Wars - he introduced the universe, our heroes, the villains and the mythology. It ended with the heroes celebrating, but Darth Vader lived, so there could be more adventures.

In 1980, Lucas started a new arc with The Empire Strikes Back. Like the first film, we are thrown in the middle of events, but it is much darker from the beginning. A lot happened offscreen in the three years between the two movies, so much so that writers Lawrence Kasdan and Leigh Brackett have to reintroduce these characters to us. Han Solo (Harrison Ford) still wants to be that selfish smuggler, but he has friends and commitments that won't let him finally pay off that debt to Jabba the Hutt. Princess Leia (Carrie Fisher) isn't a naïve idealist any longer, but a respected military commander. Luke Skywalker (Mark Hamill) isn't just a farmboy. He's grown up to be the best pilot in the Rebellion.

All those changes are put in danger right away. We don't get to spend any time enjoying our grown up heroes. The Empire is right on their trail and they can't stay safe on Hoth any longer. Peace is crushed in the first act of the film with the masterfully staged Battle of Hoth and our trio is split. Han and Luke will never be onscreen at the same time until the next movie. Luke and Leia aren't seen together for over an hour. And yet, with all these strings, this film holds together so well, thanks to the direction of Irvin Kershner.

Star Wars was Lucas' baby, but for Empire, he picked Kershner, an experienced director who had plenty of experience under his belt. He wasn't on the same level of Altman, Kubrick or Spielberg, but he was much more experienced than Lucas. Kershner pulled no punches with Empire, as if he knew that this was his one chance to put a stamp on film history. He managed to draw out performances from Hamill and Fisher that Lucas could not for Star Wars. Hamill telling Yoda, “I'm not afraid” is still chilling – partly because of Yoda's response (“You will be, you will be.”) but also because Hamill is so believable at that moment. Just three years before, Hamill was squealing about getting power converters in Tosche Station.

It's also important to keep an eye on Ford's performance throughout the film. He's Clark Gable here, playing the tender romantic scenes perfectly, but running with a powerful male role when going against Lando Calrissian (Billy Dee Williams). “I know” may be the most iconic improvised line in history and it only works because Ford understood the character so well. Even in the moment that he is most vulnerable, Han still reaches for some control. He will go into the carbon-freezing chamber with Leia knowing he understands she loves him and he's made it pretty clear before that he loves her.

Kershner not only had the two storylines – Luke training on Dagobah and Han and Leia on a date with betrayal – to balance, but he also had a third. Darth Vader is on their trail and Kershner occasionally will look in on Vader's own struggles. Try to watch Empire without having the shocking revelation in the back of your head. It seems pretty obvious that Vader has something he's thinking about that drives his decision to bait Luke into a trap on Bespin to capture him alive rather than killing the single most dangerous threat to the Empire.

I have often wondered why Empire is one of the greatest films of all time. Even after I've familiarized myself to the best that world cinema has to offer, I still think it has to be in the Top 50 somewhere. That's despite being made by a director who never earned the acclaim of his contemporaries and without the best actors who ever graced the screen.

It works because it is goes beyond science fiction. It never gets bogged down in details. Empire fully embraces film structure, bringing in the same elements of romance, adventure and danger that makes something like The Adventures of Robin Hood a great film. Sherwood Forest is no different than Cloud City, as there should be no difference. Empire is about the characters, not the world they live in. That's what the Prequels really got wrong. The audience doesn't care about the Empire's economic interests in Cloud City. We care about Lando's betrayal and its devastating effect on our heroes. If J.J. Abrams understands this, Episode VII may be in good hands.

The Empire Strikes Back is still a stunning piece of filmmaking, even if it ends in a cliffhanger, which leads to a lesser film (Return of the Jedi). It's impossible to capture the feeling of learning for the first time that Darth Vader really is Anakin Skywalker, but Empire really never ages. We return to it time and again to see how three people try to survive under the darkest of circumstances and for an ending that provides boundless possibilities.

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