Heavenly Dao Alliance is a coalition of sects in Heavenly South Region.
Heavenly Dao Alliance's acting leaders are a coalition of ten or so elders from various large sects. They are replaced in ten year intervals. This doesn't apply to the three founding sects of the Heavenly Dao Alliance. These three sects have the most sway within the alliance.
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. That's how they are capable of rivalling the other three factions.
As the Nine Nations Union had losses against Moulan Race, they requested reinforcements from Heavenly Dao Alliance, Six Devil Dao Sects and Righteous Dao Alliance. The three superpowers had to agree to not let Moulan warriors enter the Heavenly South Region and wreak havoc. This pact led to a peace in the region for a hundred of years.
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. Master Sunreach fought one of other Divine Sages. Many disciples from sects from Six Devil Dao Sects, Righteous Dao Alliance, Nine Nations Union or Heavenly Dao Alliance participated. Phoenix Cry Sect brought out their ancient jade talismans. 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.