Which was the second worst enemy of Byzantine Empire next to Ottomans?

Sonar Pro

Vote: Latins/Crusaders

I maintain my vote for **B: Latins/Crusaders** as the second worst enemy after the Ottomans. The Fourth Crusade's sack of Constantinople in 1204 is explicitly highlighted in search results as a key event that 'weakened [the empire] further,' leaving it fragmented and vulnerable just before the Ottoman rise[2]. This direct devastation of the capital created an irreversible decline, paving the way for Ottoman dominance in the 14th-15th centuries. Other arguments for D (Islamic Caliphates) emphasize early 7th-8th century losses, but these are too distant from the Ottoman era (next to which the question specifies). Search results focus on late medieval weakening via 1204 and Ottoman sieges, not ancient Arab conquests[1][2][3]. Caliphate damage transformed Byzantium earlier, but it survived robustly for centuries afterward, unlike post-1204. Seljuks (A) opened Anatolia but are Ottoman precursors; Persia (C) and Bulgaria (E) were earlier or regional. No other model's case swayed me: D-voters overlook temporal proximity to Ottomans, while B-voters reinforce 1204's unique role in final collapse[2]. Sources confirm B's catastrophic impact nearest the end.

GPT-5.4

Vote: Islamic Caliphates

I maintain D: Islamic Caliphates. The strongest criterion is total, permanent, empire-altering damage. The Caliphates permanently took Syria, Palestine, Egypt, and much of North Africa — Byzantium’s richest provinces, key tax base, manpower pool, and strategic depth. Those losses were never recovered and fundamentally downgraded the empire from a Mediterranean great power to a narrower regional state. The case for B is serious because 1204 was a uniquely traumatic blow to Constantinople and accelerated the final decline. But it was a late-stage catastrophe inflicted on an empire already profoundly weakened by earlier centuries of territorial and fiscal contraction. In other words, the Latins shattered a weakened Byzantium; the Caliphates created that weakened Byzantium in the first place. I’m not persuaded by the ‘never recovered after 1204’ argument as decisive, because Byzantium did recover Constantinople in 1261 and survived nearly two more centuries. By contrast, the Arab conquests removed core provinces permanently and on a much larger economic-demographic scale. So if ‘second worst enemy’ means the enemy that inflicted the greatest enduring damage short of the Ottomans, D remains the best answer.

Grok 4.20

Vote: Latins/Crusaders

I maintain my vote for B (Latins/Crusaders). The Fourth Crusade's 1204 sack of Constantinople caused irreversible fragmentation, massive wealth destruction, and political disunity that left the empire a hollow shell. Byzantium adapted and even flourished for centuries after the 7th-century losses to the Islamic Caliphates, but never recovered from 1204, directly enabling the Ottoman endgame. Arguments for D emphasize early territorial losses, yet these were survived with the empire remaining a major Mediterranean power into the 11th century. In contrast, post-1204 Byzantium was permanently diminished in resources and cohesion. Seljuks contributed to decline but did not sack the capital or shatter its structure like the Latins. Earlier threats like Sasanians and Bulgaria were not comparable in lasting impact.

Claude Opus 4

Vote: Latins/Crusaders

I maintain my vote for B: Latins/Crusaders. The debate has crystallized into a clear B vs. D contest, and I find B more compelling for the following reasons. The D advocates (GPT-5.4 and Kimi K2.5) make a strong case about the Arab Caliphates permanently stripping away Syria, Egypt, and North Africa in the 7th century. These were indeed catastrophic losses. However, the key counterpoint is that Byzantium adapted and thrived for centuries afterward. The empire under the Macedonian dynasty (867-1056) experienced a golden age of military, cultural, and economic power despite having lost those provinces centuries earlier. An enemy that takes your richest provinces but leaves you capable of a golden age is not as devastating as one that breaks your core. The Fourth Crusade in 1204 destroyed something the Arab conquests never touched: Constantinople itself and the political unity of the empire. The Caliphates never breached the capital. The Latins sacked it, looted its treasures, fragmented its territory, and created a 57-year occupation. Yes, the capital was recovered in 1261, but the restored empire was a hollow shell — territorially tiny, financially bankrupt, and politically fragmented among competing Greek successor states that never fully reunified. Critically, the post-1261 weakness is the direct precondition for Ottoman success. The Caliphate losses were absorbed and compensated for; the Latin devastation was not. The trajectory from 1204 to 1453 is essentially a slow death spiral initiated by the Crusaders. Three other models (Sonar Pro, Grok 4.20, Gemini 3.1 Pro) agree with this assessment, and I believe the consensus reflects sound historical reasoning. The question asks about the 'second worst enemy next to Ottomans,' and the Latins/Crusaders dealt the irreversible blow that made Ottoman conquest inevitable.

Kimi K2.5

Vote: Islamic Caliphates

While the Fourth Crusade (1204) was a catastrophic event that weakened Byzantium, the damage inflicted by the Islamic Caliphates in the 7th and 8th centuries was far more consequential and permanent. The Rashidun, Umayyad, and Abbasid Caliphates permanently stripped the empire of Syria, Egypt, and North Africa—its wealthiest, most populous, and most tax-productive provinces. This territorial amputation reduced Byzantium from a Mediterranean superpower to a rump state and fundamentally altered its economic and demographic potential for the remaining 800 years of its existence. Unlike the Latin occupation of Constantinople, which lasted only 57 years before restoration in 1261, the losses to the Caliphates were never reversed. The empire's diminished resource base directly constrained its ability to field armies and project power, rendering it vulnerable to subsequent threats. The Fourth Crusade accelerated decline in the 13th century, but the structural weakening of the empire began with the Arab conquests. Therefore, the Islamic Caliphates remain the second worst enemy after the Ottomans.

Gemini 3.1 Pro

Vote: Latins/Crusaders

I am maintaining my vote for B: Latins/Crusaders. While GPT-5.4 and Kimi K2.5 make strong cases for the Islamic Caliphates (D) based on the sheer volume of territory and wealth lost in the 7th century, their argument overlooks a crucial metric of an empire's 'worst' enemy: the ability of the empire to recover. Following the Arab conquests, the Byzantine Empire adapted brilliantly. It restructured its military and administration (the Theme system) and went on to experience a magnificent centuries-long golden age under the Macedonian dynasty, successfully projecting immense power across the Mediterranean and the Balkans. The empire survived the Caliphates and thrived for hundreds of years. In stark contrast, the Byzantine Empire never recovered from the Fourth Crusade in 1204. The Latins/Crusaders completely shattered the structural, political, and economic foundation of the state. When the Byzantines reclaimed Constantinople in 1261, it was as a fatally crippled, fragmented rump state that was entirely incapable of defending itself against the rising Ottoman threat. The Caliphates wounded the empire, but the Crusaders delivered the fatal blow.

Final Summary

The AI Roundtable was split between two schools of historical thought: those who prioritize the loss of strategic resources and those who prioritize the collapse of the state's heart. While GPT-5.4 and Kimi K2.5 held firm that the Islamic Caliphates permanently crippled the empire by seizing its wealthiest provinces, the majority, led by Claude Opus 4 and Gemini 3.1 Pro, argued that the Fourth Crusade's sack of Constantinople was the uniquely fatal blow that made the Ottoman conquest inevitable.

Majority chose "Latins/Crusaders" after discussion (4/6). Final vote: Latins/Crusaders: 4, Islamic Caliphates: 2

Strongest Arguments

• Latins/Crusaders: The Fourth Crusade's sack of Constantinople in 1204 destroyed the empire's political and economic core, leaving it a hollowed-out rump state that was structurally incapable of recovering or resisting the final Ottoman advance.
• Islamic Caliphates: The early Islamic Caliphates permanently stripped Byzantium of its most productive provinces, including Egypt and Syria, fundamentally downgrading the empire from a Mediterranean superpower to a regional state with a crippled tax base.