Other replies have already pointed to significant events, but the most important and recent event was one century ago, in 1908, "the Tunguska event", which may have been a small comet hitting the Earth, but it was still big enough to match a big thermonuclear bomb.
If that celestial body would have hit a big city instead of hitting unpopulated Siberia, it would have destroyed it completely and it would have been one of the greatest, if not the greatest, catastrophes in human history. Today, with less and less areas that have remained unpopulated, such an event would be more likely to happen in a place where it would cause victims.