Alternate History Wank: The Raj and the Russian Empire survived the meteoric winter by retreating southwards (India - Cape Colony - Australia and Central Asia). The Dai-Nippon survived in the much colder, volcanism- and tsunami-prone Japan and notoriously undercultivated China. The United States and Central Europe perished. A closer look into the plot delves quickly in Fridge Logic: USA had the warm Southern United States and Mexico to retreat, superior railroad availability, a trained reserve force of Civil War veterans already on war footing to protect the state institutions during the Reconstruction and perished, Italy had a warm climate and still got depopulated and later conquered by the Caliphate, Spanish Empire and the Portuguese-African Empire should have escaped untouched. (If anything, a general cooling of the climatewould have made the notoriously hot and dry Iberian Peninsula into a rainy fertile land.) How exactly was that meteoric winter so selective to cull only those people who would spoil the plot?
If you believe AlternateHistory.com, it's apparently the result of Stirling wanting to dance over the ruins of Western civilization. And granted, the Californians and Mormons fared somewhat better.
According to Word of God, it's the rail network that CAUSED the collapse of the US, it allowed refugees from the worst hit areas to overload the potentially surviving areas. Losing the entire east coast, including Washington to a tsunami can't have helped the coordination.
Nightmare Fuel: The Russians suffered horribly from the Fall. They've since turned into a Satanic cannibal empire in Central Asia. And let's just leave it at that. The Fall was so destructive to them that even sanity was devoured. No wonder people in the book are reluctant to even mention them. In addition to terrorizing the native Uzbek and Kazakh peoples, there's also the matter of the Sisters...
The followers of the Black God sacrifice girls (and presumably boys) in the most grisly manner, eat their hearts and livers raw, cook their flesh, and at some point Count Ignatieff admits to have eaten roast babies.
Not just admits to it, but reminisces fondly about it and looks forward to going home so he can do so again.
Uncanny Valley: Yasmini is said to have an inhuman sort of beauty, enough to scare shitless Ibrahim Khan by simply showing her face. This is the man who had no qualms to ride suspended under a speeding train in the night to get his prey.
The Woobie: Yasmini was born and raised as a slave of an apocalyptic death-cult, gets dragged around India by the main villain who treats her like dirt, fully expects to start going mad and then be forcibly 'bred', and has increasingly unpleasant fainting fits and bouts of waking dreams as the story progresses. Couple that with her frequently remarked upon exotic beauty and you have the literary equivalent of a Moeblob.
Fridge Logic: Makes one wonder why no Dreamer Sister, having the power to predict the masters' every action, never attempted to steal supplies and money from them and escape southwards toward friendlier countries.
Self-Fulfilling Prophecy: they never see themselves running south, so they never try (essentially, they are trapped by their own prophecies). Also, other Sisters would be able to tell they are trying to run away, and might actually tell on them.