There was a war between the Races and the Avatar of the planet Gaia, the humans grew tired of her arrogant and abusive ways and they all staged a rebellion. The Kingdoms had to fight against her apostles and prophets who were the forces of nature (Lighting, Fire e.t.c), the battles culled the population to 35% but in the end they won because of sheer numbers.
But Gaia in her last attempt decided to separate the world in seven different continents, so the Kingdoms ended up being separated from each other and could not interact with each other AT ALL. Millennia passes as different civilizations go to war with each other because of greed, after a thousand millennia some soon forgot of the other races until the barriers suddenly fell.
The Continents advanced differently from one another, some of the Continents advanced themselves through magic and witchcraft while other civilizations had a technological evolution. Each continent was like an entirely different world.
When the barriers fell some of the races had no idea of how to communicate with each other and thus conflict ensued. The Elven kingdom brought peace between the demi human races and soon brokered a treaty between the humans as well.