A single large comet, 20 to 30 miles across, doesn't have to hit intact to cause catastrophic damage. If it breaks apart on approach, the fragmentation alone could produce a million objects the size of the Tunguska impactor that exploded over Siberia in 1908. That one event released energy equivalent to a 15-megaton hydrogen bomb, 15 million tons of TNT. Had it detonated over any populated area, that city would have been obliterated. The structure of a comet nucleus makes this scenario not only possible but plausible. When you consider the physics of breakup during atmospheric entry or tidal disruption, you're not dealing with one impact. You're dealing with a cascade, a barrage that could blanket entire regions. Some fragments could be even larger than Tunguska. This isn't speculation. It's what the mechanics of cometary disintegration allow for, and it's a scenario the geological record may already contain evidence of.