Not one big enough to cause another great extinction, but small enough to just turn a whole small country and parts of neighboring ones into a huge crater. Will the people who was evacuated out after NASA stated a warning try to rebuild the country after everything has settled down or do they’d become citizens of another country?
Edit: after reading the comments, maybe turning a small country into a crater is too much, what about just level the place, or in any way that make it uninhabitable for a period of time?
I mean you could probably wipe out Lichtenstein or Vatican City with conventional munitions that wouldn’t endanger the planet.
An asteroid that is small enough to contain the impact to Vatican City would probably burn up in the atmosphere and wouldn’t hit. It would have started off at about the size of a car.
The asteroid that created Barringer Crater was probably about the size of a football stadium, that’s the kind of asteroid that is needed to destroy your average sized small country.