In the late 1st century BC the Republic had become pretty much disfunctional. It was prone to infighting, greed and class warfare, and could barely deal with the problems of the day. Several critical issues, such as land reform and what to do with soldiers that had completed their service, festered for decades without any solutions. Violence erupted frequently. Civil wars between generals were frequent. The Republic was almost always in crisis, and it struggled to govern the large empire won by Rome through several wars in the 3rd and 2nd century BC.
The Republic was plagued by civil war between ambitious generals. The republic lacked a strong executive to prevent such civil war. The Empire was better equipped to deal with this problem.