Why was the concept of one world or the unification of all people important to persia

They had no tolerance for other cultures, so they made their conquered peoples to adopt the Persian culture.  

Explanation:

The Persian civilization was one of the most significant civilizations of antiquity. Persia was located east of Mesopotamia, on a large plateau where it now corresponds to Iran, located between the Persian Gulf and the Caspian Sea.  

The Persians conquered many peoples who lived near the highlands of Iran, imposing the same administration and customs on all, creating the concept of "one world". They eventually built a vast empire. Its territory comprised Asia Minor, Mesopotamia, and a part of Central Asia.

under god i have placed my chiest strentgh and the safe guard to my loyal subjects