Humans evolved a long time ago. They developed supernatural-seeming abilities of control over elements. It started with the basic elements: fire, water, earth, and air. People quickly used these abilities to gain power and then the elemental nations formed. They were a meritocracy, led by whoever was the most powerful in that element, although they were usually aided by the smartest people of their element if they weren't the smartest themselves. If you weren't naturally born especially strong, you could work your way up the chain of authority by studying and honing your craft.
When the nations formed, it became very taboo to have contact with members of the other nations outside of work or politics. It was unheard of to have relationships with people of another element, much less have children with them. Often the person's element had a large effect on their personality, so they wouldn't have likely gotten along even if it wasn't taboo.
There were still, however, a few outliers. The Romeos and Juliets who found a way to make it work. This was when they discovered that mixing elements created a child with a complex element. This ended up uniting the nations. Bearing a mixed child was reserved for politics. If the water nation and earth nation wanted to make a deal, they would oversee the creation of a mixed child who would be a gift to the nation that was getting the worse end of the deal. These complex elements could get strange. Water and earth once made a child who could control life itself and healed many before being assassinated by those who were threatened by him. Another child of water and earth could be able to control plants, or perhaps just mud though. There were many more possibilities for the element of a mixed child.
Eventually the fire nation started growing. The invention of the steam engine and the dynamo meant that a fire elemental who could heat up water could also power their home for as long as they lived. This meant that they developed much quicker than many other nations. They also had an advantage in war. They took land from others and led the world in strategic innovations. In order to plea for peace with them, the earth nation offered many mixed children.
The fire nation asked for four of them, and the earth nation agreed. The first was a child who could control lava, the second a child who could control gunpowder, who became a military leader, the the third was a child who could control lava as well, but the last child was peculiar.
The fire nation, after the disappointment of a second lava elemental, requested that the earth nation negotiate an air and fire mixed child as a proxy for the fire nation. The earth nation would only get their peace if they could convince the air nation to give up a child of their making.
They managed it, and the fourth child that the fire nation received was one that could control electricity. This child also happened to be both smart and powerful, which led to him becoming the leader of the fire nation, even though he was not even an official citizen. They all looked up to him and respected his wisdom. He also became the leader of the air nation for the same reason. For the first time two nations came together as one.
There was a large influx in mixed children and this led to a very quick advancement of the already advanced nation. The water and earth nations were left in a near stone age, while the fire and air nation invented computing, radio, and mass production.
The society of this nation was much more open to mixing and ended up accepting the water and earth nations to join them.
The world was finally at peace for a time. They were all led by a single government that was a panel of the most powerful of each element and they voted as representatives of each element. Each elemental government still had their own land, but now they were a part of a larger government that became known as the United Elements.
This led to mixed children being able to have children with other mixed children. These advanced elementals were found to have increasingly unique powers, such as control over light or magnets. The less powerful and the less intelligent of these went on as normal, maybe becoming a business owner if they were successful. The powerful and intelligent ones, however, became a serious force. An electromagnetic elemental who was completely powerful became the next leader for a long span of time. They were capable of controlling the entire electromagnetic spectrum, so not just controlling magnets or light, but radio signals, microwaves, infrared and heat, visible light, ultraviolet, x-rays, and even gamma radiation. Luckily, while he was able to control a vast amount of things because of his power, this trade off meant that he could not have a very large scale, like a jack of all trades. A powerful and smart person focused on visible light could have made illusions of entire armies, or made entire armies invisible, but he could instead do this only for maybe one soldier.
Cal hoped that he would be like him. He flipped the page in his book about the history of the elements. Tomorrow he would turn eighteen and he couldn't stop thinking about the possibilities. Over his entire senior year of high school he had to watch most of his friends find their abilities. His best friend Josh ended up with electricity, but he was very powerful. His other friend Sarah, got healing, which was really a mild version of the life element that that child was assassinated for, but nowadays as long as it is mild people keep them around because they can save lives, but not take them.
He had skipped 4th grade, because his teachers thought he needed more of a push, so he was only 17 for senior year, but now he was at the same college as Josh and Sarah and would finally get to show them what it would be.
He put his chemistry book in his bag, and made sure he had his notebook for calculus and then put it on and ran out the door. Josh and Sarah were at the bus stop. "We were worried you slept in." Josh laughed.
"Nah, I was just packing up my stuff. I got a little carried away with reading about elements. I turn 18 tomorrow!" He said excitedly.
They both chuckled. "Yeah, we go that the last three times you told us." John said.
"I'm sure you will have an amazing power and you are such a nerd that you will probably end up as a government leader or something." Sarah said to him.
He shook his head. "I just can't wait to know what it is, at this point I don't really care what it is, I just want to know." He explained.
The bus came and picked them up and took them the short distance to campus. They all lived in the same housing complex off-campus.
Sarah waved to them and went to her class, while Josh and Cal continued to their calculus class. The day went by dreadfully slowly for Cal. All he could think about was the endless possibilities for what tomorrow would bring. He mostly daydreamed through his classes and then finally got back on the bus with his friends and they spent the rest of the day hanging out in Cal's apartment, playing video games and placing bets on what they thought Cal would be.
"Five bucks says that Cal is another one of those radio wave guys, but the kind that can do all sorts of stuff like microwaves and all that." Josh said.
"I'll take that bet." Sarah shook his hand. "I think he is going to be a water elemental, but a very powerful one. You've seen him swimming and all that."
"Ah shit. Good point." Josh nodded and frowned, now worried about his bet.
"Yeah that's what I was thinking it would be." Cal told them.
They played some more and also congratulated Sarah about her new job at the campus hospital. At about ten, Sarah and Josh left back to their own apartments and Cal tried to sleep, despite his overwhelming excitement.