The Ten Great Devil Dao Sects from Great Jin cultivate true Devil Dao techniques from antiquity. There are far more pure and ingenious, unlike those of Six Devil Dao Sects from Heavenly South Continent, which seem to be superficial. 
There is a late Nascent Soul cultivator in the Six Devil Dao Sects, the Righteous Dao Alliance and the Nine Nations Union, each only a step away from entering Deity Transformation stage. This is how each of the three superpowers remain on equal footing. As for Heavenly Dao Alliance, they have two mid Nascent Soul-stage Dao Companions that are proficient in cooperative techniques.
War with the Seven Sects of Yue
Six Devil Dao Sects secretly invaded State of Che Ji and Jian. Many members of the two country's sects and clans were bribed. As a result, with an ambush of formidable strength and the aid of several traitors, the two countries fell quickly.
Then they invaded the State of Yue. The Seven Sects of the State of Yue defended well. At the border shared by the State of Yue and the States of Jiang and Che Ji, over ten great battles had occurred there, resulting in the deaths of over ten thousand cultivators. After allied forces from States of Yuanwu and Zi Jin arrived, invasion was resisted. The war sunk into a deadlock and became a battle of attrition. As a result, large decisive battles became less frequent while smaller scale surprise attacks more frequent.
After betrayal of Spirit Beast Mountain, the Six Devil Dao Sects had great victory and the Six Sects of the State of Yue and allies from two other coutries suffered great losses. The State of Yue was in great turmoil. Despite that, some cultivators of the Six Sects, including Core Formation experts, survived and were still fighting, impeding with the Devil Dao's takeover of the State of Yue.
As the Nine Nations Union had lossess against Moulan Race, they requested reinforcements from Six Devil Dao Sects, Righteous Dao Alliance and Heavenly Dao Alliance. The three superpowers had to agree to not let Moulan warriors enter the Heavenly South Region and wreck havock. This pact led to a peace in the region for a hundred of years.
After the Six Devil Dao Sects and the Righteous Dao Alliance had discovered a withered ancient Profound Goddess's Palm near the Moulan Plains, they made a plan to acquire the Spirit Well Tree to restore it. Disciples from Thousand Illusions Sect, Heavenly Fiend Sect and Righteous Dao's Overwhelming Pavilion were send to infiltrate the three sects in the Dreamcloud Mountains to acquire the Spirit Well Tree. When they used the Wine Nectar to water the Profound Goddess' Palm, the tree remained in its withered state without change.
After about 100 years, Moulan tribes launched an invasion. After loss of Soaring Heavens City, reinforcements from the Righteous Dao Alliance, Six Devil Dao Sects and the Heavenly Dao Alliance had arrived and stopped further progress at the border between States of Yu and Beiliang.
The final battle involved hundreds of thousands of cultivators. Long Han served as the commander of the Heavenly South Army and Divine Sage Zhu commanded the army of spell warrior. Devil Concord fought Yin Sifting Sect Master Fang. Many disciples from sects from Six Devil Dao Sects, Righteous Dao Alliance, Nine Nations Union or Heavenly Dao Alliance participated. Before the culmination, Moulan received news about the attack of Soaring Tribes. Both sides stopped fighting. With peace talks against the common enemy, Moulan got 2 countries near the border, and the Nine Nations Union was compensated with other territories.