The Douluo Continent is one of the two continents that humanity was born on, on the Douluo Planet. The other one being the Sun Moon Continent. It is the largest out of the present three continents. Before the events of SL2, the Sun Moon Continent collided onto the Douluo Continent, linking the two continents.
It was the home of many kingdoms and empires as well as many different sects and schools. The most noteworthy are Shrek Academy and the Tang Sect. It is home to a wide variety of spirit beasts and different natural environments like the extreme northern lands and the Star Dou Forest. It's because of this that the Douluo Continent has the most number of spirit masters.
In Soul Land 3, with the rapid development of humanity, spirit beasts are on the brink of extinction and the natural resources on the continent are being depleted, causing the environment to deteriorate. If this continued, the continent would have been destroyed. This lead to the Abyssal Plane and other planes attacking the Douluo Planet. The Continent faced a life crisis during the first invasion. The Continent was almost destroyed during the second invasion, but thanks to the ten thousand year planning by Tang San, the Eternal Tree was able to absorb the life energy from the Abyssal Plane, causing the Douluo Planet to evolve and allow spirit masters to cultivate beyond rank 99.
In Soul Land 4, the Douluo Continent was replanted with countless planets and flowers, improving the environment and the quantity of life energy on the Douluo Planet.