There are theories which say that nuclear war, due to firestorms in cities transporting soot into the upper atmosphere, would lead to nuclear winter, which would lead to a global famine:

https://forum.effectivealtruism.org/posts/pMsnCieusmYqGW26W/...

However, the papers which predict such scenarios have been criticized as being too pessimistic:

https://www.lesswrong.com/posts/jnDibtfvWNHLucf4D/actually-a...