Popes achieved supremacy because no Western monarch matched Byzantine imperial power.

Evidence

In the West, but not in the East, the laity were mostly illiterate for many centuries, and this gave the Church an advantage in the West which it did not possess in the East. The prestige of Rome surpassed that of any Eastern city, for it combined the imperial tradition with legends of the martyrdom of Peter and Paul, and of Peter as first Pope. The Emperor’s prestige might have sufficed to cope with that of the Pope, but no Western monarch’s could. … For all these reasons, the emancipation of the Pope from Byzantine domination was essential both to the independence of the Church in relation to secular monarchs, and to the ultimate establishment of the papal monarchy in the government of the Western Church. — Bertrand Russell, History of Western Philosophy, 1520

Categorization

• XREF: XREF: Explores the institutional centralization of Western Christendom versus the East. — connects to: Gregory established Western papal authority by exploiting prevailing anarchy and personal ability — Bertrand Russell, History of Western Philosophy, 1499; Medieval legitimate power depended on the mutual dependence of pope and emperor. — Bertrand Russell, History of Western Philosophy, 1526; Some Orthodox Christians preferred Ottoman rule to papal supremacy — Ali Qureshi, The Fall of Constantinople: A Critical…, 23 (+1 more)
• corroborated: 2 independent passages support this claim — Bertrand Russell, History of Western Philosophy, 1520

Broader Connections

• Medieval legitimate power depended on the mutual dependence of pope and emperor. #corroborates (0.60) — Bertrand Russell, History of Western Philosophy, 1526
• Ottoman control preserved Orthodox autonomy while Latin control demanded papal supremacy #responds-to (0.55) — Ali Qureshi, The Fall of Constantinople, 26
• Some Orthodox Christians preferred Ottoman rule to papal supremacy #responds-to (0.50) — Ali Qureshi, The Fall of Constantinople, 23