On my list of the most important "events" I think the two World Wars would come first, for the profound changes they have engendered or gave momentum to: communications, transportation, media & propaganda, moral & existential philosophy and beliefs, the shaking of religious faith, science (esp. physics, and eventually the space race) etc. It also brought to an end the colonizing era, and drastically changed the political world map.
Urbanization and the internet brought parallel and profound changes, I believe. Education and information are now more available than ever. For millions, it has also been a huge change of lifestyle. And arguably increased isolation in the ever-expanding global community.
Then there are those changes whose importance depend on point-of-view, i.e. changes that were felt more locally. For example, the atomic bombing of Hiroshima and the humiliation of defeat changed Japan dramatically, from a war nation to an economic superpower. The end of their empire allowed other Asian nations to develop too.