Conversion of the Romans and the Bible's Portrayal of the Romans

I have trouble understanding how the Romans converted to Christianity. In the Bible, the Romans weren't portrayed very nicely. For example, Herod the Great did quite a lot of awful things. Jesus was crucified by Roman soldiers. The Bible obviously seems to portray the Romans as the enemy of the Chosen People of God. It doesn't make a lot of sense to me that the Romans could still become Christians. [I want to apologize ahead if my questions sound disrespectful to anybody. This isn't my intent. I grew up in East Asia which has very few Christians. I have been studying the Bible on my own. My knowledge could have serious defects and my terminologies could be way off. I would appreciate if you guys can bear with me, and help me understand the history and the Bible better.]