Final answer:
The lack of an organized system for imperial succession in the later Roman Empire caused political instability, military-focused leadership, neglect of governance, and weakened responses to external threats.
Step-by-step explanation:
The later Roman Empire faced significant challenges due to its lack of an organized system for imperial succession. This deficiency led to political instability, as the throne was often contested through assassination, military force, or by other means such as the auctioning off of the Imperial title by the Praetorian Guard. Rival factions within the Empire vied for power, resulting in turmoil and civil wars which detracted from Rome’s ability to manage both its domestic and international affairs effectively.
When succession was uncertain, it generated periods where military generals assumed the title of emperor, but their focus on self-preservation and war campaigns meant neglect for other crucial aspects of governance such as state finances, building campaigns, and religious worship. This neglect could cause the governmental machinery to grind to a halt, especially when communications were slow, leading to governmental inaction and delayed responses to crises.
External pressures, such as the rising Sassanid Empire and increasing threats from better-organized barbarian groups, exacerbated Rome's vulnerabilities. Without a stable succession plan and the frequent change of leaders, Rome's military and political systems struggled to cope with these external threats, leading to lost battles and territory, further degrading the confidence in Roman leadership.