Actually, the reason why the Netherworld Realm army had managed to invade the Earth Emanations Domain so easily was related to the Ten Thousand Domain Tournament. It was also connected to the Earth Emanations Sovereign's absence from the Earth Emanations Domain.
The battle on Heaven Camel Mountain the previous time had led to the killing of a ten-million-year-old Chaos Beast and countless Chaos Beasts that had been demonized by the Netherworld Realm with the aid of the Earth Emanations Sovereign. Three god bandit militia bands that were secretly being controlled by the Netherworld Realm had also been eliminated.