Alternate history writing prompt

http://www.independent.co.uk/news/science/the-end-of-the-world-as-we-know-it-1999537.html

Every century or so, a 10-meter meteor slams into the Earth with the force of a small nuclear device. Tunguska was the site of the last, in 1908, and it was pure luck that that meteor landed in the uninhabited wilderness of Siberia.

What would the world be like today if the meteorite had hit 18 hours later and flattened Washington, DC? (Or Austria, killing Hitler, or Moscow, killing Lenin and returning the Romanovs to power…). What’s more, what if the blast that destroyed a capital city was claimed by someone to be their work with a superweapon?