Size of asteroid/comet compared to effect on impact

In an Earth-like world I have long pondered building up, the pre-industrial (roughly colonial) society primarily exists on a single continent, roughly the size of Africa. Another continent has been discovered, and an early colony has been settled there.

This world has multiple moons, which in a freak event are aligned just right as a comet (or a meteor) passes between them, that the gravitational forces break the object apart. The resulting fragments rain down on the primary continent, causing damage, and setting civilization back a ways, but not completely obliterating it. (Leaving the new-continent colony temporarily more technologically advanced, and opening a plot for them to go back and see what happened)

What size comet or meteor could fit this type of criteria? I lean towards comet more because of their porosity, and a bit of 'wow' factor if it happened to be seen as it approached, but a meteor is acceptable if a comet is not plausible. It needs to be large enough to cause a major blow to a continent, but not so large as to completely wipe out all life on it - perhaps (most) cities would shatter and crumble, but some pockets of life will survive.

(I am aware of This Question but it seems to focus on city-sized effect, rather than continental, and I can't figure out how to work the simulator linked therein to meet my request)

posted over 8 years ago

Rayanth‭

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