It can also be called "Aquilon Republic". The Aquilonian is the most civilize and technological advance nation in the world.
They are located in the far north, on the other side of the Great Desert (commonly called "The Desert"), the largest desert in the world. The north generally has hot weather, due to many natural factors, but with their great technology, the Aquilonian has air-conditioner systems that no other civilizations have had.
The other side of the Desert used to be a big secret, until the Iron Eagle's agents successfully crossed the desert and found out many things on that side. They went on to scout the Aquilon and eventually found out a horrible truth: The Aquilonian has tools that can kills quickly and easily from far away. They called it "gun" and "bullet"! They also have other inventions for warfare like bombs, stun guns, fire guns, electrical knives, electrical whips, artificial animals, artificial monsters, etc.
After realizing that the Aquilon Republic is so far more advance than the rest of the nations on the other side of the Desert, the Iron Eagle's scouts tried to return home but only one of them survives. Most of them are killed by the Aquilonian guns, some of them are killed by the Sahara Tribe on the desert.
The one who survives informed the news to his boss in the Iron Eagle. The Iron Eagle informed the King. The Zuda's Imperial Court decided not to keeps this news as a secret. They gave this information to their ally, the Kazen's Imperial Court. The two kingdoms eventually decided to inform the whole world about this threat.
From that point on, the Republic of Aquilon became a common threat and common enemy of every empires and kingdoms south of the Desert. Every emperors and kings feared one day the Aquilonian eventually will be crossing the desert, shooting, firing and destroying everything in sight.
It takes decades to develop a few wizards, sorcerers and witches, or fighters who know how to use magic. However, it only takes couple of months to equipped guns for millions of people.
It's extremely difficult to find a talent who has the potential, mental attributes, work ethics and all the requirements to be developed into a wizard. Most have failed.
Whereas in Aquilon, they already familiar with the technology, making guns is easy. A weakling with a gun can kill an experience warrior or even a wizard who learned magic since childhood.
So, why doesn't the Aquilonian just crosses the desert and conquers the world?
I. The Aquilonian has spies, too. They know the countries on the other side of the desert are lacking unity. If they advances to the south and conquers, the countries would join hands and unify to fight against the common enemy. They are waiting for the countries to go to war, killing off each other. After that, they will come and take care of the rest.
II. They still need more guns and bullets. The resources have its limit. They currently don't have enough guns to fight all those nations.
III. Contrary to popular belief among the people on the south side of the Desert, the Aquilonian do have some major weaknesses. They do struggling with their own problems. For instance, the internal fighting between the Senate (15 members), President Electra and the Prime Minister Davis. All sides tend to reject each other ideas and proposals. Therefore, they rarely commit to anything, rarely got anything done.
As the economy grows, corruptions and inequality also grow. The tension between the upper class and the lower class continue to rise. Many workers and students have protest, some protests turn into chaos and violence. Many countrymen and peasants have joined rebels. Many teenagers joined gangs, criminal organizations and many underground organizations. Some even joined the terrorists.
There are also some resistances and independent movements from the natives and the colonists.
IV. The Great Desert and the Sahara Tribe are obstacles that make the journey to the south extremely risky. They can chase away the Saharan in Aquilon. However, on the desert, the Saharan has great home field advantages. The Aquilonian surely don't want to be trapped in the middle of nowhere, surrounded by sands and the heat. They also don't want to get ambush.
Even if they managed to get to the other side, they still would have to deal with Martia Kingdom, the most violent and aggressive nation on the other side of the Desert. The Martian is the most war-ready kingdom in the region.
Also, previous regimes in the north had built the Long Wall, castles, forts, traps and other defensive constructions in order to prevent the Aquilonian from advance to the south. Every nation on the other side considered the Aquilon Republic as their greatest threat. The fear of the Aquilon is the only thing that keep the nations from warfare. They have been able to maintain peace for decades now.