We've mostly been analyzing societies as isolated entities, and if it hasn't been obvious, I've been mostly referring to the United States in particular, apologies for the looseness of the language. But things get much more interesting on the global level, when these societies - with their subtle and not-so-subtle differences - interact with each other.
Over greater timescales, it gets even more interesting. The question has been posed here before: what in the world is a civilization anyway? We tend to think of a civilization as geographically bounded and rooted, which can be true for all sorts of historical geopolitical developments.
For example we talk about Western civilization, or Classical civilization, or Chinese civilization, and then even those designations melt down and we start to talk about empires and ages in the same breath: the Ottoman Empire, the Mongol Empire, the Bronze Age civilizations, etc. Though depending on your source, you get better consistency of the language and concepts.
And then these supposedly distinct entities profoundly influence each other, and fold into each other, and break apart and re-constitute within each others' bounds, and leave behind stores of knowledge, technologies, cultural interests and artifacts, and so on which influence and assist others in turn. And then there is the issue of the circulation of individuals and who constitutes what society or civilization and where are they going and what will they be?
There is a broader question about what a majority of the world population is doing, and doing together at a given time. Today we have all kinds of continuous cultures around the world, though global capital has so suffused international relations, it has transformed the societies it penetrates and then linked them tightly together through international supply chains and divisions of labor.
Eventually those tightly bound links of international trade will sever and then everyone will become something else in their own ways.
