There wasn’t a single cause. The Western Roman Empire unraveled over centuries and formally ended in 476 CE when the general Odoacer deposed the last western emperor, Romulus Augustulus. The Eastern Empire (Byzantium) continued until 1453. Major, interacting causes for the Western Empire’s fall included:

- Political instability: frequent coups and civil wars, short-lived emperors, and weak central authority undermined coherent policy and defense.
- Military strain: defending an enormous frontier, recruiting troubles, growing reliance on barbarian federate troops, and field armies diverted by civil conflicts.
- External pressures: the Huns’ expansion displaced Germanic peoples into Roman territory; Gothic, Vandal, and other groups established kingdoms within former imperial lands; sacks of Rome (410, 455) and the loss of North Africa (439) crippled revenue and grain supplies.
- Economic deterioration: heavy and uneven taxation, currency debasement and inflation in earlier centuries, disrupted trade, and a shrinking taxable base.
- Administrative overreach and division: governing a vast, diverse empire proved costly; the permanent split between West and East (395) left the poorer West without the East’s fiscal depth.
- Demographic and epidemiological shocks: major plagues (Antonine, Cyprian) and local famines weakened manpower and resilience.
- Cultural and institutional change: shifts in civic identity and priorities (including but not limited to religious transformation) altered how resources and loyalty were mobilized—debated by historians and not a sole “smoking gun.”

In short, long-term structural weaknesses met acute external shocks; the proximate end in the West came when the army and resources could no longer sustain imperial rule.
