For a major capital city Berlin is still poorly served with mostly 2-stop connections from the US
Berlin is poorly served by USA carriers (only United). However, I would say the majority of the USA has 1-stop service available to Berlin.
1) airBerlin flies to ORD, JFK, and MIA from Berlin Tegel. It is important to note that not all of these are daily during off-peak times.
Serving ORD alone technically gets you the majority of the country 1-stop via codeshare with American Airlines.
2) UA flies Berlin-Newark but not daily during winter.
3) If your city has a London Heathrow, Paris, Amsterdam, Frankfurt, or Munich flight your connected one-stop.