Okay ... let's look at those 1400 years. Start of the Greek city states. Greece counts between several dozen to hundreds of religions. 500 year later, 3 big re

Okay ... let's look at those 1400 years. Start of the Greek city states. Greece counts between several dozen to hundreds of religions. 500 year later, 3 big religions left. Roman republic + empire, starts out with hundreds of religions. When it ended ... 2. 200 years after it ended, only one religion really survived it. Or you could take Africans in America. At one point African genes were pretty much the only genes of 18% of the population of the United States. Currently, about 2% of Americans have majority African genes, a number that's dropping exponentially (but obviously only once per generation). But as I said Google "island species" and read around a bit. It is part of the original theory of evolution, described by Charles Darwin, and pretty much the only part that has survived almost unchanged. Essentially, diversity can exist where large natural barriers separate different groups, so that when individuals copy eachother, they copy, imperfectly, one of their own group. Because small errors make the groups drift apart, diversity occurs. The result is that an ethnic barrier gets created along the natural barrier. When the barrier goes away, because of technology, climate change, military conquest, or a natural disaster, so does the ethnic and/or ideological difference. It does not go away by merging both races or ideologies, it goes away because one of them dies out, to be replaced by the other. Needless to say, modern technology has been tearing down most of those barriers. If the result is diversity, that will be the first time in history, but it is plainly obvious that there is nothing all that different between the current time period and previous time periods where for some reason populations mixed. The result will be the same : only one culture survives.