Climate change and disease affected the Sassanian and Roman Empires in various ways. Climate change led to droughts, crop failures, and famine, which weakened the empires' economies and their ability to fund their armies and maintain their populations. The empires were also affected by pandemics, such as the Plague of Cyprian and the Justinian Plague, which caused widespread death and social disruption. These pandemics further weakened the empires by reducing their population and undermining their ability to maintain their borders. The empires faced increased pressure from external threats, such as nomadic invasions and Arab conquests, which ultimately contributed to their decline and fall.