The Catholic Church faced a series of problems threatening their religion. The two major problems was there was no unity within the churchy, and another problem was that Rome who was at peace with all religions was going against christianity because of their determination to dominate over all other religions.
Religious Tolerance For all!!
The Roman State eventually declared war on the Christians with hopes of defeating them physically and mentally. The martyrs in the church were not symbols of defeat, but they were signs of encouragement within the growing church.
During the war Constantine had a vision that told him to put Christ's image on the shield. He did this and after every single battle that ended victoriously was devoted to Jesus.
He is now emperor and is making an agreement with emperor milan to have religious tolerance. (religious acceptance)