At The National Interest, Ted Galen Carpenter writes (abridged):
Given the political division of the Korean Peninsula and the tensions it has generated over the past seven decades, the danger of an armed conflict involving North Korea and its neighbors is ever present.
America becoming entangled in such a conflict because of its security guarantees to Seoul and Tokyo is the one credible scenario that might culminate in a North Korean nuclear attack on the United States.
A similar risk is building in the Middle East, where the United States has foolishly injected itself into Iran’s quarrels with both Israel and key Arab powers such as Saudi Arabia.
Again, the likelihood of even a nuclear-armed Iran launching an attack on the American homeland out of the blue is highly improbable.
A war between Tehran and one or more of its adversaries that spirals out of control and snares the United States because of Washington’s implicit security commitments to Israel and/or Saudi Arabia is, unfortunately, a much greater danger.
U.S. leaders can retain a high level of confidence in the reliability of direct deterrence. But extended deterrence in both East Asia and the Middle East entails an already excessive—and rising—level of risk.
Read more here.