China, pretty much any period sees retardedly ancient weaponry used alongside the most modern. Choice picks include the Warlords Period and Taiping rebellion.
The Early Modern Period in Europe, around 1400-1650s, which saw medieval armies and knights in full plate fight against and slowly homogenize into pike and shot, with lots of interesting mad inventions along the way, like the first breech-loading gunpowder weapons, multiple-barrel firearms, bulletproof armour etcetera, even attempts at reintroducing the longbow as late as the 1640s.
>>639992
Proto-Jews (possibly Canaanites) caused the Bronze Age Collapse, as I recall the banking networks among the civilisations first promoted the use of mercenaries over standing armies, then denied loans or withdrawals to the states, causing the sea peoples (the mercenaries) to loot and pillage and generally set off the first large scale vikingr invasion