They had the support of the church, the military was loyal , they had a strong claim.
They might have failed at waging war properly. (Napoleon in Russia 1812) They couldn't deal with the revolts (French revolution), they might have brought an economic downfall to their country.
They might have expanded lot. (The roman empire was the largest under emperor Trajan)
they let people build great buildings. They commissioned musicians to perform masterpieces
