The kingdom of Kadsia is under the Empire of Chronoa. The empire of Chronoa is known for its excellent magic technology. The magic technology improves every year no matter what.
The magic tech was pretty useful for a long time, which helped to compete against other empires. But now magi-tech is on the decline because of the new emperor.
There are 4 empires on the continent of Demacia. They are the rulers of this continent. And they have been fighting for sole supremacy of the continent for years. But for now they are at peace.
The four empires Onyan where the elves live, Nongan where the dwarves live, Anima where the beastmen live, and Chronoa home of the humans.
John is from the empire of Chronoa.
Since the empire of Chronoa's magic technology is declining. The emperor of Chronoa decided to force everyone to go to a magical institution at the age of 15
Being a mage has always been john and Aelin's dream, so this was an opportunity for them.
So they are happy that they had this opportunity to train to be a mage because only nobles and a select few of commoners with high talent could go to. A magical institute.
So they vowed that they would be the strongest of mages.
To survive in this world.
In this world where the strong eat the weak they would only be cannon fodder if they don't get stronger.