If we take the terms separately:

تأصيل: formalization
منهجي: methodical

the translation would be:

"methodical formalization"

and the phrase would be:

... and I performed a methodical formalization of the concept of ethnic communities.

That seems acceptable, but too literal. Other alternatives:

... and I introduced a formal representation of the concept of ethic communities

... and I established a formal definition of ethnic communities.

Hope this helps,

Alaa Zeineldine