How did the rise of constantinople contribute to roman culture

It's because Roman culture did not disappear because the traditions were kept alive by leaders in Constantinople.
You can see that many features in the city of Constantine is made based on the design that was taken from the Roman period and the interior usually filled with Roman artworks. Not only that, many ceremonies and celebrations is being done based on Roman tradition. 

Because he proposed that all the treaties should be made through the league of nations.