I can answer this to some extent for the Islamic world, particularly greater Persia, with the caveat that we know far less about the peasantry than we do about urban dwellers.

As a general rule in the Middle Ages (prior to the Mongols) the conquest of territories was by the latest and greatest band of Turkic horse nomads who, while practicing Muslims, did not speak the local languages, Arabic or Persian.

As such there was a reliance on the Ulema (religious scholars) in a given city to mediate between the new rulers and the community of believers. This resulted in a great deal of continuity as the practices of taxation, rule of law, etc, would hardly change. It had the effect that despite constant warfare and the turnover of huge tracts of land that actually these territories could continue to prosper.

This was only increased by the iqta system. The iqta can be contrasted with feudalism in several ways, although there were multiple types of iqta the military iqta is probably the most relevant. Here, commanders of the nomadic forces were given the taxation responsibilities for large tracts of land, but the appointments, at least in theory, came from the sultan and therefore feudal relationships of responsibility never developed. The Islamic lands also did not practice serfdom, so when faced with an injustice governor who taxed the people unfairly, the peasants could simply up and leave.

The Mongols are a total break from this. The institutional mediation that more or less insulated the peasantry and the urban notables from the effects of regime change disappears. Simply put, you can't mediate the Mongols, at least at first.

Whole cities are wiped off the map, and although we can't be sure of the numbers, it's clear that cities like Nishapur are just gone. Regardless of the accuracy, the accounts are at least interesting. After apparently insulting one of the Khans, the citizens of Nishapur, all 1,000,000 of them, are beheaded and their skulls arranged in a massive pyramid.

Eventually however, the mongols have the same problem that the turks did which is that they don't speak the language, they have no experience in administrating settled peoples and they have to seek out the help of the local populace. This is sped up when the Mongol Khans convert to Islam. Eventually you have the vizier Rashid al-Din who is the vizier to later Muslim khans and actually writes history casting aspersions on the early mongols as having not followed Islam, having mismanaged the settled lands of the state, having abused the people etc. etc.

Sources: I'm a big fan of David Morgan Medieval Persia: 1040-1797 and the relevant portions of Marshall Hodgson's The Venture of Islam