When the Roman Empire split, the eastern part of the empire was made into the Byzantine Empire. Therefore, they adopted many of the rules, like the twelve tables, but adjusted them. Also, when they split, the Byzantine Empire adopted the Greco-Roman language.
Diseases that they were never exposed to, such as smallpox, killed close to 90% of the population. With most of the opposition to the domination gone, the Spanish could easily sweep in and conquer who was left.
