What do you think is the MOST important Byzantine achievement? Why?

One of The Byzantine empire's great achievements was the preservation of Roman and Greek Culture.

Explanation:

In 476 in the West, the Romans collapsed. Along with their downfall, many libraries and other documents were lost. The Byzantine Empire survived in the east, along with the rest of the Roman Empire. They attempted to save as much information and knowledge that they possibly could. One of the major documents that were preserved was the Roman Law because it was written by Byzantine's greatest emperor, Justinian. Justinian was able to figure out what the Roman Laws meant and he also focused on the existing laws. Because of Emperor Justinian, the Roman laws are the base of our government and the government of other countries.  

Most significant was the preservation of Roman law by Emperor Justinian, the Byzantine's greatest emperor. ... Cultural Diffusion - Not only did the Byzantine help preserve Roman and Greek culture and Christianity but the Empire also spread these ideas to other parts of the world

Explanation:

the answer is

a) revise existing treaties

b) do away with political alliances

c) prevent the spread of communism

d) bring an end to european colonization

the main goal of the southeast asia treaty organization was to prevent the spread of communism in southeast asia.

this question does't support enough resioning to answer.