NOTE: THIS WAS ORIGINALLY A RESPONSE TO ZIRYERX'S COMMENT BUT DECIDED TO MAKE A BLOG ON IT BECAUSE IT SEEMED LIKE AN INTERESTING QUESTION! ALSO THOUGHT I SHOULD MAKE THIS SINCE THE CURRENT KORRA ERA IS BASED ON THE 1920s. YOU ALSO DO NOT HAVE TO AGREE WITH THIS.
Cultures change drastically and new trends could come up. For example, the new series might be set in a 1930s setting or a 1940s setting. Also since the Korra era is based on the 1920s, it'd be cool to see a formation of the Avatar universe's League of Nations.
The 1930s was the Great Depression, the rise of Nazi Germany and Communism, prohibiton in the US, war with Japan and China, the fall of the League of Nations and the beginning of World War II. Though, I highly doubt that the next Avatar show would have another World War, especially since the Hundred Year War was a mix of World War 1 and 2 and the real Hundred Years Wars of England and France.
the 1940s was a majority of World War II, the fall of Nazi Germany, the end to many wars like the Japan and China war, the rise of Communism in China resulting in Civil War turning China communist, the beginning of the Cold War and the hostile tensions between the US and USSR and of course, the rise of Anime in Japan.
The 1950s or 1960s would be great too since in the 50s, it was all about the fear of Communist take over and in the 60s, we were afraid of nuking each other so we started a sub-culture of people who desire peace and love over war and even went to the point of protest against war an violence. We also put a man on the moon.
the mid 1960s to the early 1970s was war with Vietnam and afterwards in the reast of the 1970s, it was like a much more advance 60s but with less Hippies and more pop culture and rock.
the 1980s, holy crap, the 1980s was basically when pop culture took over the world and everyone started dressing up in colorful clothing and the music and films were catchy, it was also a time of dept and the final decade of the Cold War.
the 1990s was like a much more advanced 80s but pop culture was less involved and the fall of a government and nation, the Soviet Union, occurred and the restoration of the old government formed.
the 2000s was the decade of paranoia and fear, mostly in America, towards Terrorism and the efforts to destroy terrorist groups and a decade long chase for a single man. It was also a time when technology became much more apart of the lives of people and started to become something much more than originally thought. It was also a time when National security tighten and the Government began getting paranoid of both terrorism and the rise of the internet.
the 2010s is obviously our current decade and while we're still in it, we can clearly say that this is the Digital era of humanity, with the internet now being one of the most important parts of not just lives, but buisness, governments and spying. It was also the fall of terrorist groups and the rise of paranoia towards the government with recent events like the leaks of U.S. NSA's surveillance files on people of the USA and other countries like Germany, the United Kingdom, China, Russia and South Africa. Not only spreading distrust and anger towards the nations but also causing tensions between all the nations the US spied on and of course, the rise of Anonymous, which would be perfect villains for the Avatar in my opinion.
There is so much material and huge events in our history for the creators of Avatar can take as inspiration for the series, and this is just from an American point of view! A lot of it might have trouble fitting in, but I think the 1930s - 80s eras would blend in with the Avatar world much smoothly, especially the 60s. Also, to those who might think adding these would destroy the nature of the show, it's only inspiration, it doesn't have to be completely adapted. Hell, they might even mix eras, like mixing the 50s with the 2000s or the 70s with the 30s. You also don't have to agree on this.