His soldiers went from divine kingdom to divine kingdom killing and pillaging. The pillaging didn't stop until every god had died. Even the divine city was looted. He took the bulk of the wealth while his dukes and their subordinates helped themselves to what was left. And that's only because it wasn't worth the effort to take them himself.
There was so much wealth that the looting took a few days before it was completed. It is wealth that would have made Ancestor Ghastorix whistle in admiration. If he had this, then he wouldn't have had to sell out his descendant for a world engine.
Origin gods are wealthy but it costs a lot to resurrect the more powerful they are. They fight a lot and they die a lot which drains their resources. Getting more resources also won't happen without fighting which will further lead to more deaths. So rarely does an Origin god come into contact with this kind of wealth.
Aeternus considered the wealth and nodded in appreciation. He said to himself, "This will fund our project and ensure that it will be ready as soon as possible."
He attacked the divine plane for a lot of reasons. The Celestial Godhoods will help to strengthen the tree father. It is particularly important that the tree father is strong enough to manipulate the amount of energy that they are using to build their project.
As for reaching the next rank after Celestial, that is still a long way to go. They don't even know if it is possible. The tree father has accumulated about 100 domains spread across his avatars. They won't know if that is enough until he fuses them back together. But they have to be sure because there might not be a way back once they are fused. So they are accumulating as many Celestial domains as possible for the tree father.
The wealth that Aeternus has acquired will also be used to fund the different parts and research for the project. Salvini tried to hamper Soverick's attempt at acquiring wealth but she failed because she failed to account for the other clones.
Aeternus has been raiding divine planes for their wealth all for the project that the whole of Legion is working on. It is a project of immense significance. Legion-1's inner world is being combined with his knowledge of arrays and formations, Soverick's forging expertise, the tree father's energy manipulation and transmutation ability, Legion-7's expertise with the soul and law manipulation abilities, and finally with some other powerful parts like a world engine, Authority of a Celestial Supreme, Celestial Godhood and World Spark.
What they are building is technically a world fragment but it will be more powerful than that. It will be another class of weaponry on its own. It is very powerful but it also needs a lot of materials for the project. What they are doing is unprecedented. Soverick and the others have to do research and sometimes they fail. Failure leads to a loss of expensive material.
So Aeternus is doing his part in bringing the Artifact to completion by contributing wealth. That's not why he brought two demon kings to take the plane with him though. He can take on the divine plane on his own but he brought along two weak demon kings that he can kill.
Despite how it looks, he didn't lure them here to be killed. He even gave them information about the Celestials so that they wouldn't be killed in battle. No matter what, they must not be killed in this plane.
That's why he captured one demon king instead of killing him after being rightfully provoked. It was the snake demon king who tried to steal from him and who attacked first. He is only defending his interest. He also let the other one go despite her being sneaky and scheming. One might say that he is being generous and reasonable. Anyone who says he is devious and scheming will also be right.
Aeternus finished the looting then he waited for his soldiers to leave the divine plane. He waited for all of them to return to the abyss before he himself left. Some of them went to his plane but most of them went to other planes of the abyss. Most of his direct subordinates are demon lords. He gave them another competition where the aim was for them to go and subjugate an abyssal plane by themselves.
The competition with Beelta as the kill target needed all of them to work together because they were not as strong as Beelta individually. So he beefed them up with some divinity and sent them to kill other demon lords and take over the energy pillar of the plane by themselves. Those who failed to do it within the deadline were hunted and killed by his heralds.
So he has a lot of demon lords as subordinates. The ones that haven't become demon lords yet are still new. They need time and resources to become strong before he sends them out to become demon lords. He will raise up their stats to the maximum level and then send them off to invade a plane on their own.
Demon dukes are the equivalent of demon lords so his subordinates aren't strengthened directly when they become demon lords. But the house of chaos is strengthened which gives a boost to everyone within the house.
This boost is a result of his ability called Divine House. He also gets to control the resources of multiple demon planes. It has made sure that his army is always full for all the invasions he has been having recently.
A single abyssal plane can provide hundreds of billions of battle-ready mid-rank demons so more than 50 planes are supplying him with trillions of soldiers. He never lacks in soldiers because of it. Some of them are returning to their plane now. While the ones from his plane and his heralds will return to his own plane.