In 330 BC (the year of the fall of the First Persian Empire), 65 percent of humanity was worshipping three Gods: Vishnu, Ahura Mazdā, and Zeus. Here’s my analysis:
In 330 BC, the population of the Persian Empire (which included the Middle East, and parts of North Africa and Central Asia) was 50 million. The population of the Indian subcontinent (then dominated by the Nanda and the Maurya Empires) was 100 million. The population of those parts of Europe which were influenced by the Greeks, Macedonians, and the Persians was 10 million. The human population on earth in 330 BC was 250 million.
Thus, in 330 BC, 65 percent of humanity lived in the Persian Empire (Ahura Mazdā was the chief deity), the Indian Subcontinent (Vishnu was the chief deity), and the Greek, Macedonian, and Persian influenced parts of Europe (Zeus was the chief deity).