First, a quick clarification: historians usually mean the fall of the Western Roman Empire (conventionally dated to 476 AD, when the last western emperor Romulus Augustulus was deposed). The eastern half — the Byzantine Empire — survived until 1453. The “fall” of Rome was not a single event but a long, messy process caused by many interacting factors. Major causes commonly cited are:

- Political instability and bad governance
  - Frequent civil wars, short-lived emperors, usurpations, and court intrigue weakened central authority and drained resources.
  - Division of the empire (Diocletian’s Tetrarchy, permanent split into East and West) made coordination harder and left the weaker West more vulnerable.

- Military problems
  - Continuous pressure on frontiers from Germanic tribes, Persians, and later the Huns forced heavy military spending.
  - Recruitment problems: fewer Roman citizens serving; increasing reliance on foederati and mercenary barbarian troops whose loyalties could be uncertain.
  - Decline in discipline and effectiveness of some units over time.

- Economic troubles
  - Heavy taxation to pay for the army and administration, which hurt agricultural productivity and commerce.
  - Currency debasement and inflation undermined confidence in the economy.
  - Trade contractions and loss of wealth in the West compared with the richer East.

- Social and demographic change
  - Population decline from plagues (e.g., the Antonine Plague), lower birth rates, and war reduced manpower for agriculture and the army.
  - Growing inequality and erosion of civic elites who traditionally ran local government.

- Invasions and migrations
  - Large-scale movements of peoples (Goths, Vandals, Franks, Burgundians, Lombards, etc.) pressured frontiers and sometimes entered as refugees, allies, or conquerors.
  - Key events like the Gothic sack of Rome (410), the Vandal sack (455), and the deposition of Romulus Augustulus (476) were symptoms and accelerants of collapse.

- Administrative overreach and structural problems
  - The empire became territorially and administratively overextended; bureaucracy grew costly and sometimes inefficient.
  - Local government weakened as central control frayed.

- Cultural and religious changes
  - The rise of Christianity changed cultural and institutional patterns; historians debate how much this directly undermined Rome’s civic institutions. Most modern scholars view it as one factor among many, not a primary cause.

- Environmental and long-term structural factors
  - Climatic shifts, soil exhaustion in some regions, and changing trade routes likely contributed to agricultural and economic stress.

Historiography and nuance
- Modern historians reject simple single-cause explanations. The fall is best seen as a long-term, multi-causal process in which internal weaknesses made the Western Empire increasingly unable to absorb or repel external shocks.
- Debates continue over which factors mattered most (e.g., military vs. economic vs. migratory pressures); recent scholarship often emphasizes the interaction of migration/invasion with internal decline.

Short summary
- The Western Roman Empire collapsed because long-term internal weaknesses (political instability, economic decline, social and demographic stress, and administrative difficulties) combined with sustained external pressure from migrating and invading peoples. The collapse was gradual and complex rather than the result of one single cause.

If you want, I can:
- Give a concise timeline of key events from the 3rd to 5th centuries,
- Summarize major historians’ interpretations (e.g., Gibbon, Peter Heather, Bryan Ward-Perkins), or
- Explain one of the causes in more detail. Which would you prefer?
