Chapter 752: BATTLE BETWEEN WORLDS (1)

Disk Formation had a lot of restriction in fighting in the world because of the Article of Distribution. 

While this make them able to live a peaceful life, it also hinders their training in battle. Since each Disk Formation is prohibited in fighting against each other they could not gain experience.

They could spar of course but they have to spar far away from Earth. 

Not everyone has the free time to go to fight in a distant star and not everyone could find a person that they could spar with.

Right now, it was like the restriction has been lifted. The world is being attacked, and so titans and giants of the world are coming out to kill all invaders

That is the exception of the rule. 

In the Article it is mentioned that if the world is being attacked by other worlds, Disk Formation powerhouse could ignore the rules to dispel the invaders and is responsible to do so.