Revelation from On-High (Heaven, that is) has apparently been known to occur. However, it surely is a rare event; and may be unreliable (while unverifiable).
The transfer of learning and of new ideas, or new cultural practices and their underlying belief-rationale, occurs through enduring exposure. For example, the diverse peoples of Southeast Asia became acclimatised to Hindu religious practices and their associated belief systems through ongoing contact with Indian traders; later, the latter’s priests (who, unlike Christian priests, do not seek to proselytise and convert) would also have had an impact through the observed display of their rituals.
Emperors and other militarists are, by their very roles and actions, not known to be effective transmitters of durable new cultural practices and associated values. Their ambassadors have a political role, including reporting to head office their observations on their new temporary environment.
Traders move on their own trajectories, unless paid to be spies. Together with settlers from other cultures, they have a pervasive effect on the people they encounter, but without intending to change anything. In this context, I am reminded of Megasthenes, the ambassador to (Indian) Chandrangupta’s Empire from Seleucus, the successor in the Middle East to Alexander the Great. He made some very interesting observations.
Ironically, Alexander reportedly sought to adopt, without success, certain court practices of Persian royalty. Perhaps the priestess in Siwa (Egypt) had confirmed his alleged belief that he had been sired by a god. The adoption by officials of the British East India Company of the traditions of their predecessors, the Mughals, was however so successful that they were criticised by England’s class-riven rulers as ‘going native.’
When a tribe changes religion by fiat, by the ruler’s decision (for example, the Khazars of the Caucasus and the Singhalese of (modern-day) Sri Lanka), would the cultural changes have involved more than a change of religious belief? The conversion by British evangelists of some Indians and Ceylonese did not appear to have altered their behavioural values and practices in the Asian communities I observed; only religious observance was amended.
Naturally, in time, for a variety of reasons, cultural practices will change. My extended family is an excellent exemplar. I recall a visiting academic from Greece in Melbourne in the early 1980s who was criticised for saying that. He had pointed out that Athenian cultural practices had changed over time; and that island culture, which was not the same as Athenian culture, had also changed. Somewhat unwisely, he had wondered (as I understood him) whether one could really talk of Greek culture.
In truth, is any culture uniform across a people? There are classes, castes, and sub-cultures in countries which are familiar to us, eg. Australia, Britain, Japan, Malaysia, India.
Culture is indeed a moveable feast. In modern times, a degree of fusion between hitherto separate cultures can also be expected. What value is there in cultural competition or aggrandisement?