One major challenge that Diocletian faced was that the Roman empire was extremely large and it was growing fast. Diocletian solved this by creating the tetrarchy, splitting the Roman Empire. He gave one half of the empire to be ruled by Maximian. Diocletian was the emperor in the East and Maximian was the emperor in the West. Another challenge was a war around the Danube river.The war in the Danube river was finished by defeating the Sarmatians in 286 CE. This brought some peace to the Roman emperor. A third challenge was who was going to rule after Diocletian. Diocletian solved the problem of his successor by creating tetrarchy. This meant that any four people ruled an empire. The last problem was the growing followers of Christianity. The last problem of  growing Christianity was solved by a long persecution. Anyone who didn’t make a sacrifice to the Roman gods would be killed.