What wa the problem with the military (private armies)during the time of the republic ?

While PMCs often provide services to train or supplement official armed forces in service of governments, they can also be employed by private companies to provide bodyguards for key staff or protection of company premises, especially in hostile territories.

Explanation:

powers  are  denied  to the  national governmentin three distinct ways: some  powers, such as the  power  to levy duties on exports or prohibit the freedom of religion, speech, press, or assembly, are expressly  denied  to the  national government  in the  constitution.