Summary
Somewhere between 1000 CE and 1200 CE is my guess. Maybe like late 900s, but I don’t actually know. I’m basing this off of “it’s early than most people would probably expect” and figure most people would be guessing like 1500 CE+. China had them well before the rest of the world did.
Guns or firearms? The exact definition matters here I think. The earliest forms of cannons were probably created in less than a century after the proliferation of gunpowder, and I cannot imagine it wasn’t used for weapons, generally, more or less right away. Like cannons were likely playing a not insignificant part of any military battle where a side had them. Taking my lowest estimate for “invention of guns” of 1000 CE, guns (specifically some kind of cannon) began to play a major role in some military battles somewhere in 1100-1200 CE. If we’re talking about firearms, I’m gonna guess like 1500-1600 CE depending on your definition of “being a major part”. Standing in a line and shooting at each other style warfare is probably in 1600-1700 CE.
Uh. Depends on what you consider plate armor I guess. The earliest form of plate armor is probably like 1000 BCE out of bronze. Armor like the kind we imagine knights wearing probably didn’t show up until like 1000 CE+, but plate armor, generally, has been around for a very long time.
Yeah idk you’re gonna get me on this one probably. Like 300 CE to 1200 CE. Jeanne 'dArc. Charlemange. Crusades. Black plague.