This can be considered a sister question to this question.
Outside of Ser, the world was a chaotic and dangerous place. Ser was the only neutral country in a world filled with violence and devastation. In 1515, there were at least 8 wars going on and nobody had any alliances. All trade was cut off.
The country Ser, led by an aging Empress Ana, was self-sufficient and had access to plenty of resources. She said:
Let them fight, die, or whatever it is that barbarians do with one another. There is no need to intervene, so long as they do not cross our borders.
A New Emperor
In late 1519, the Empress died from illness and her son gained the throne. He had a much different opinion of the world:
The world is crying. Who will wipe its tears? Who is there to aid when all are possessed?
The Dominance Declaration
In 1521, he declared war...upon everyone. He stated that he intends to rule all people and in order to do so he must unite all countries into a single government. It was a seemingly impossibly foolish move that would probably cause the destruction of the entire country.
As of this moment, the Ser Empire will begin to liberate the people in the world burdened by their oppressive governments, who forfeited their right to yield power when they abused it. We will extend our hand in leadership towards these victims and one by one, we will unite all of mankind. This will be the last war.
In response to this, nearly all of the countries that were all once enemies of one another forged temporary ceasefires in order to defeat the Ser Empire, whom they viewed as foolishly arrogant. They called themselves the "Truth Bringers."
You are no God. We will bring to you this truth.
Winning the War
In only four years, the Ser Empire managed to conquer all enemy territories while simultaneously defending their own from all attackers in every direction.
Here comes the question part: The next section details how I explain the basic strategies of the war. I want to know just how realistic it is, or whether the Ser Empire would have actually been completely annihilated.
During the war, the Ser government utilized the wars of other countries to its advantage, slowly gaining allies by promising regulated trade and by watching as the countries with temporary ceasefires turned on one another.
For example, they deliberately conquered the region of Ferockana early on in the war because its government was already involved in four wars of its own, and this gave the Ferockana militia an incentive to fight alongside Ser in order to defeat their own enemies.
In addition, Ser settled the disputes of conquered nations by offering compromised trade so that former enemies could fight together in newfound peace. With an exchange of goods or land that they previously denied each other, each nation profited significantly from the arrangement.
Ser's main strategy involved conquering and negotiating. Basically, they show the enemy that they can't win. Then, instead of destroying the enemy, they said "Join us, and we'll do this for you." Not only that, but the Ser Empire promised to intervene in the conquered nation's affairs as little as possible, in addition to giving them access to resources that they otherwise would not have been able to get.
They deliberately went after the countries that had the most to gain from joining them first, such as Ferockana which was in 4 wars of its own.
Join us, and those four countries won't stand a chance.
They also went after the country that had advanced herbal medicine and medical technologies first, which in turn helped keep the soldiers healthier than the other invading armies.
How feasible is this strategy for world domination? Is there anything I am missing to make this work?
Technology Clarification: Ser also had more advanced technology than the surrounding countries. The world was living similar to the 1500s, but the technology of Ser was probably similar to the 1700s.
Guns that used gunpowder were not widely in use at the time but were still available. The Ser emperor pushed for the development of better weapons. For example, muskets were in use but were improved to allow quicker reloading and better aim. Ser also developed the first gun capable of shooting multiple projectiles simultaneously: it was originally called the scattershot, but was later called the shotgun.