Over the millennia, any civilization or cluster of cultures will have had its ups and downs. But when you overlap the world’s major ones on a single timeline like this:
or
Was there a particular century (or thereabouts) where multiple civilizations across the world were simultaneously experiencing major events? Even better if they were somehow intertwined, with multiple events that started independently culminating in a perfect storm that stretched across borders.
Of course, there’s a lot more of that once we approach the modern era, especially after the world wars. But what about before?
Did the major empires ever cross paths unexpectedly? Could a wayward merchant have carried news from one part of the world to another, “Did you know that in ______, X is happening right now?!” Or even if the two cultures weren’t familiar with each other at the time, were there any periods that later historians would identify as especially important to both?
If you’re asking for centuries, then it must be the twentieth. Two world wars plus a cold war plus first increasing colonization and then the decolonization that has already been mentioned. Plus technological and economic progress hitherto unseen. Affected the entire globe very profoundly.
I don’t see how there’s any debate about this. The 20th century changed the world more than all previous centuries combined. Perhaps to be surpassed by the 21st century which may end before the world wide collapse of all prior achievements.
One overlap of misery was when the Mongols burst out of the Steppes and impacted the lives of everyone from Vietnam to Hungary. The Ottomans rose in their wake, closing the Eastern trade routes the Europeans, who’d sail the Atlantic as a recourse; impacting the lives of the Western Hemisphere.
Because, IIRC, a Byzantine princess was Ivan the Terrible’s grandmother, the Czars claimed a direct line to the Roman Empire. The Russians colonization of bits of Alaska made that, technically a world-wide empire. (Or, if the Holy Roman Empire was a more legitimate heir, Spain’s holdings under Charles V in all over the place too)
Another fascinating overlay (though more in terms of connecting seemingly unrelated things, not in terms of importance in the greater scheme of things) is that Charlemagne, the first emperor of the Franks (a realm that later evolved into the HRR) exchanged envoys and gifts with Caliph Harun ar-Rashid, of Arabian Nights fame.
An overlay that has had a profound impact on global history is the fact that it was the conclusion of the Christian Reconquista of Spain that enabled the Spanish kings to fund Columbus’ first voyage.
