This is a book about fear (p. 3).
Both the Ottomans and the Hapsburgs had learned lessons from the Thirty Years’ War (p. 62). Ottoman army units were much more autonomous, typically composed of men who were related to one another. Austrians were more top-down, relying on brilliant generals who viewed their units as abstractions (p. 64).
The Austrian side was vastly outnumbered, with about ten thousand able-bodied men compared to 50-80 thousand Turks.
Disease affected the besieged city. Some polish mercenaries and Austrian regulars who entered the city just before the Turks arrived brought with them a disease known as red flux. As the siege dragged on, all stray cats and many rats were eaten by citizens (p. 150). Fortunately for the Viennese, there were no fresh outbreaks of plague during this time.
Vienna was both a bastion against and a connection to the Islamic world (p. 189) as exemplified by the fact that coffee houses were quickly established in the city after the siege was lifted, using beans left behind by fleeing Ottoman troops.