Through ancient and medieval history - the steppe as a driving force seemed to disappear in the modern era, though you can say its influence was only transposed - the settled societies would record their interactions with the steppe peoples with a mix of suspicion, disdain, irritation, awe, and admiration, but these feelings would come at a sort of remove: we were situated and set-fast here, they were over there doing what they do.
But eventually these relations tended to spill over. We've already talked about the waves of Germanic migrations, set into motion by climate change and the movements of the Huns, those Hunnic movements having a distant genesis of their own.
And then on into the Middle Ages, with the successive movements of the Vikings, eventually establishing kingdoms of their own, and the movements and establishing of kingdoms of the Mongols in the east. And the Turks coming in from the east and sweeping into the Arab Muslim world, adapting Islam and then Europeanizing in turn as they clashed with the Byzantines, overtaking them while establishing the Ottoman Empire, which would take root in that cracked shell of Constantinople, with a new urban capitol coming into being as Istanbul.
Not to make light of these successive human catastrophes, but a lot of these common processes bear a resemblance to the paradoxical regenerative capacity of wildfires, sweeping through existing societies in their paths, whether they were in a decadent phase or not, breaking them up into simpler constituent elements to eventually be recombined, containing the DNA of both conqueror and conquered.
Besides the crosspollinating effects of the various trade networks connecting distant settled societies, you had nomadic peoples like the Goths and the Vikings traveling all over Europe, and in the case of the latter, far into the east and then even across the Atlantic to North America, moving slaves back and forth, intermixing, spreading technologies and culture and technique.
You could see in the turbulent course of the collapse of Rome and the subsequent germination of the early medieval world a sort of "smashing together" of that nomadic vigor for movement and dynamism and the settled society's preference for stability and deep, sustained technological development. To simplify, those tall walls and fortresses that would eventually typify the medieval castle - a lot of steppe societies weren't good at siege warfare, though the Huns and Mongols were notorious for being quite adaptable with it - probably looked pretty good to nomadic chieftains growing tired of constant migration and warfare.
Other than the Polynesian societies, the Vikings were some of the first to venture out into the open ocean. Whereas many previous societies could utilize quite advanced ship designs, they usually stuck to coastlines or at least stayed within visible range of land, when they weren't blown off course by bad weather or strong currents.
In keeping with this, many earlier empires were land based - albeit with their various trade networks branching out through water-routes - so it was probably not a coincidence that we would see the culmination of this "smashing together" in the British seafaring empire, which developed in a particularly vulnerable region in which there was a constant clashing and crosspollination of the nomadic and settled societies.
Lest we want to prematurely place human values on this process - I am loathe to call any of this "good" or "bad" - we could fast forward to the Industrial Revolution, that unprecedented explosion in technological development, mobility, and material power, taking place in that superheated cauldron of Western Europe, which created a problem or two for every problem it solved.
Plenty of economic thinkers like Marx would look to create a little lemonade out of them sour-ass lemons: "Well, capital has socialized the means of production, so we might as well make use of that." Though at the same time, today one can't help but nervously eye those belching smokestacks as things continue to heat up.
