Human-Demon Wars

The Human-Demon War (人魔大戦 Jinma Taisen) were three wars fought between the Demon Race and the Human Race. The first two wars were waged by Great Demon Empress Kishirika Kishirisu, known as the Great Human-Demon War, to reign superiority over the Human Race. But the third war was waged by Demon God Laplace in his own name, referred to as the Laplace War, as an outcome of his hatred of the Human Race.

First Great Human-Demon War
The First Great Human-Demon War (第一次人魔大戦 Daiichiji Hito-Ma Taisen) is the first great war between the Human Race and the Demon Race which was fought between 6000 - 7000 years prior to the main story. Kishirika Kishirisu, the Great Demon Empress, and the Five Great Demon Kings led the Demons against the Humans. This war was fought before the splitting of the Central Continent and the Demon Continent, when the Humans and the Demons still lived in one landmass known as the Great Continent. The war lasted for approximately a millennium, repeating constantly between a state of fierce battle and relaxation. Finally the hero of humanity Ars and his six comrades ended the long war following the defeat the Five Great Demon Kings and the Demon Empress Kishirika.

Second Great Human-Demon War
The Second Great Human-Demon War (第一次人魔大戦 Daiiniji Hito-Ma Taisen) is the second great war between the Human Race and the Demon Race which was fought between 5000 - 4200 years prior to the main story. The Great Demon Empress Kishirika Kishirisu, seeking vengeance for a thousand-year old grudge, brought the Beast Race and Ocean Race to the Demon side and waged war for the second time against the Human Race. This time the Human Race was pushed back and cornered but the war still went on for several centuries without surrendering.

At the time of distress of the Humans, the Demon Dragon-King Laplace joined the war to annihilate the Demon Army singlehandedly which allowed the Human Army to retake their frontlines. Laplace was eventually defeated by the Fighting God who was an Apostle of Hitogami. On the verge of death, Laplace performed the reincarnation Magic of the Dragon Race but the spell went out of control and the released force of Mana was so strong that it split the Great Continent into two - now known as the Central Continent and the Demon Continent - forming a new sea in the middle now referred to as the Ringus Sea. This event marked the end of the Second Great Human-Demon War which lasted for 800 years.

Laplace War
The Laplace War (ラプラス戦役 Rapurasu Sen'eki) was a war that lasted between 500 - 400 years prior to the main story. Though it lasted much shorter than the previous wars, the humans were forced into a war far more brutal than any they had fought before. The one who united all the Demons of the Demon Continent and launched this assault against the Humans was the Demon God Laplace - a human-hating Demon who was split from the failed reincarnation attempt of Demon Dragon-King Laplace in the previous war.

Demon God Laplace spawned approximately a thousand years ago. In a extremely short period of time, he rallied the Demons and conquered the Demon Continent. For many years he cultivated his empire, building his race to be tough and fierce. After long years, he pulled the Beast Race and the Ocean Race over to his side.

Laplace began his military campaign approximately 500 years ago. The invasion began from the south, drawing all the humans' military power there. Then he set his wyrms upon the land, making passage through the mountains impossible. After that he took the humans by storm, attacking with a separate unit from the north, scattering his enemies. In a short time, he had gained total control of the north and the south. Then from both directions, he pressed his assault on the western region.

Forced into a corner, the humans took their last gamble. The Seven Heroes convinced the Ocean Race to lift their blockade, then set out on the seas for the Millis Continent. Now allied with the demons, the Beast Race had taken control of the Holy City of Millis. So the Seven Heroes took the clan leaders' children hostage and threatened them into cooperation. The Seven Heroes, leading the Holy Knights of Millis and the Beast Race, launched a decisive battle and assaulted Laplace's main stronghold.

After a violent confrontation, four of the seven heroes were dead, but they successfully sealed Laplace away and destroyed his closest companions. Though Laplace was defeated, the humans were greatly exhausted from the long battle and couldn't keep up to fight anymore. Instead, they signed a treaty with one of the Demon Kings who wasn't allied with Laplace and the blockade on the Demon Continent was lifted. According to the terms of the treaty, racial discrimination was prohibited and demons could now freely travel to other continents.

Trivia

 * Demon Dragon-King Laplace joined the human side of the Second Great Human-Demon War under the false name of Aldebaran who was nicknamed the Golden Knight.
 * Demon Dragon-King Laplace, who was a Demon-Dragon hybrid, split into two beings after his failed reincarnation attempt - Technique God and Demon God. Technique God retained his Dragon Race side and all his knowledge; Demon God retained his Demon Race side and his hatred for the Human God, eventually forgetting the "God" part his hatred mistakenly turned towards the Human Race itself.