People seem to forget that the final collapse of the Han Dynasty, the collapse of the Parthian (Iranian) Empire, and the Crisis of the Third Century in the Roman Empire all happened within a fifteen year period (220-235CE).

Although the Han Dynasty started coming undone in the 180s, there was a cooling period in East Asia and North East Europe that started around 200CE and lasted for most of the century. It isn't difficult to imagine a macro linkage between cooling -> agricultural output -> instability that was exacerbated by a similar reduction in Eurasian trade due to the global transition of power (in 200CE, the land route for the Silk Road was effectively controlled by four powers - the Roman Empire, the Parthian Empire, the Kushan Empire, and the Han Dynasty... this fragmented dramatically, particularly in East and Central Asia, by the end of the century).