There's no need, who would willingly pit their military strength against Zhou Tian's!
Thus, when Zhou Tian had shown off his million-men strong army back then, it actually had already proven his ability. Seeing his movement, many forces decided to retreat immediately.
No matter if they still need to fight with Zhou Tian or not, Zhou Tian being able to display such strength was already proof of his deep foundation. Hence, no matter if Zhou Tian wins or loses later, the forces that can participate in battles related to him must possess a certain degree of strength.
Whether Zhou Tian or another force wins, the winning side which would collect the spoils of war or get a share of the spoils would need a certain degree of strength. If they inherently don't possess such strength, forcefully intervening in Zhou Tian's battle might result in them not gaining any benefits, but instead, be wiped out by Zhou Tian and his forces.