What was the most important impact of the jewish peoples’ repeated diaspora?
a. it fractured the people and their beliefs.
b. it created tension with king cyrus.
c. it drove the kingdom into serious debt.
d. it spread the religion into europe.

The most important impact of their diaspora's was that they were able to spread faster throughout Europe, compared to other religions or even any diseases. Because many Jews fled to Europe and fled to all the different parts of Europe, more and more people were infected with the idea that this religion was right for them and the only true one. 

For that reason, the answer you're seeking is D - it helped spread the religion into Europe. 

♥ d. It helped spread the religion into Europe.
Spreading the religion into Europe was important to the Jewish people. 
Therefore this was the biggest impact.