Christopher Columbus accidental voyage to the Americas.
Reason; it led to expansion of civilization to 2 other continents.
Roman Gallic Wars; Beginning of Roman expansion northward.
Reason; Rome brings civilization to central & northern Europe for the first time, all the way up to modern day UK, where Romans build Londinium, modern day London. Romans also built every other capital in modern day Europe at this time.
5th Dynasty Egyptian trade.
Reason; along with trade, ideas and a massive culture exchange occurred, Egypt brought civilization to the Mediterranean. Herodotus, Europes first historian, stated that even ancient Greek religion derives from Egyptian religion. The Olympian gods are re-named Egyptian gods. Zeus is Amun. Hades is Set, etc.
Notice, I [and everyone else commenting] is giving you historical phenomena from a western perspective. I am certain there were other comparable important events I have not stated, like the political event that brought civilization to China, Japan, India or the middle east. If you truly want to be objective you must recognize that you are educated on the perspective of where you're from.
World wars and the cold war were important events but much less so, they are simply geopolitical conflicts between superpowers, something as old as history itself, and with no significant effect.