In 330 BC (the year of the fall of the First Persian Empire), 65 percent of the human population on earth worshipped three Gods: Vishnu, Ahura Mazdā, and Zeus. Here’s my analysis:
In 330 BC, the population of the Persian Empire (which included the Levant, and a big slice of North Africa and Central Asia) was 50 million. The population of the Indian subcontinent (then dominated by the Nanda Empire and the Maurya Empire) 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.
This means that 65 percent of the human population in 330 BC 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). During this period the kingdoms fought wars on all kinds of political and economic issues, but never religious ones.