During the early 1990s, what event shifted the focus of the army's activities toward the stopping old rivalries and conflicts?

It is the separation of the Soviet Union into littler states. The Soviet Union was disintegrated on December 26, 1991. It was a consequence of the assertion number 142-Н of the Soviet of the Republics of the Supreme Soviet of the Soviet Union. 

Beforehand, from August to December, all the individual republics, including Russia itself, had either withdrawn from the union or at any rate criticized the Treaty on the Creation of the Soviet Union.