Y'zaks was once defeated in his homeworld. As a powerful demon king who used to command several demon races, he had always been a leader whom his followers worshipped. After Helcrown landed on Aerym, Y'zaks resigned from the throne and ordered several respected regents to be in charge of domestic affairs until his daughter reached adulthood. Nevertheless, he was still the highest authority in the kingdom. Soldiers would rally behind him and ready themselves to attack any target without hesitation should he command it.
So, when Y'zaks ordered Lanina to gather the troops, Lanina only asked two questions: where to attack and how many to kill.
The warriors under the mad demon king's command would never ask anything outside those two questions.