A global storyline is one that will appeal to the largest number of people on the planet. That means the Latin world, China, India, Europe, Japan, Africa and the U.S.
We have to appeal to members of all major faiths and the even larger number of non-faith people.
Let's look at what Avatar has in its storyline.
1. Divinity. Star Wars had The Force, an awful lot like the Christian God. Avatar has an animistic divinity (Eyra). The reality of the world is that in Latin America, parts of Africa and the Philippines Catholicism is patched on top of animism. All of Africa is animistic with very little gloss of religion on top. Japan and China are purely animistic. Europe is Eco-apocalyptic which is an abstract animism the successor to Paganism. India is much harder to categorize but there are so many local deities that it is probably close to animistic. So Avatar has a global divinity message that is right on target; Star Wars missed the boat.
2. Good-Evil. Star Wars had a clear good-evil split from the beginning to the end. Good-evil seems to be a global reality. Avatar has the additional great theatrical benefit of character development and a change in the viewer's perspective. The viewer of Avatar starts out on the side of Good and changes through the movie to the other side and finally is convinced that the original good is evil; a much more dramatic storyline.
3. Warrior. Warriors are heroes around the world. Both Star Wars and Avatar are story-lines built around a warrior hero. In both cases it is a man of ordinary qualities who grows during the film, and under the duress of the storyline, he grows into a hero.
4. Necessity of war. Nearly everyone in the world (maybe not the Japanese these days or the Norwegians) realize that power, strength and often war is necessary for survival. Being good is not enough. Star Wars and Avatar are war stories based on the clash of good and evil. No story would succeed without the necessity of a war between good and evil. The global film market demands it.
5. Romance. The American view of romantic love is popular everywhere... often as a superficial notion (the real force in most of the world is still arranged marriage). No sex on screen is acceptable in the global market; a kiss maybe. What Avatar has that Star Wars didn't have is a warrior woman as the romantic love object. That may just be a change in the times since the 1970's. Star Wars, for those who forget, was a romance with a Jewish-American princess.
6. Good people. On this subject Star Wars got the subject of good people wrong. The good people were dwarfs (Obi-wan Kenobi and R2D2). In Avatar the good people are correctly ten feet tall. Most of the world (not the Chinese and Japanese) considers tall people to be superior to short people. The good people in Avatar are tall but blue. I have no idea where blue is a good global color.
7. Science. Most of the world is anti-science as was demonstrated by the total failure of the Copenhagen Global Warming conference. Cameron, the Avatar producer, couldn't have known about Copenhagen but his film gets anti-science right. The scientist dies and renounces science as she dies. Star Wars was neutral on science.
Cooperation. In the end of Avatar, the Good people organize all their neighbors in a cooperative military assault. Most of the world theoretically values neighborly cooperation. This is obviously not a high value in the fractious parts of the world such as Arabia, Africa, Latin America and many other non-democratic locations but cooperation is valued in theory.
Under dog triumphs. This is one element of the storyline that most of the world supports. That element is in both Star Wars and Avatar but much of the global population doesn't buy it. I'm thinking of China, Japan and Arabia where the the top dog is usually right, not the underdog.
Is Avatar anti-American? In the end, the evil military-corporate side resembles America. But if you look at the list of values I've just listed you will see that Avatar is a triumph of American values. We can sell tickets to anti-Americans, but the moral message of the film is wonderfully American.
Put simply, one can read Red Ridinghood as a children's story about not trusting wolves, or more intelligently Red Ridinghood is about the dangers of the world, the forest and straying too far from home alone. Avatar is really about triumphant American values.
Summary. A global film success needs a global storyline. I've outlined most of the elements of a global storyline. Avatar has all I can think off.