Hello,

Ottoman History MA here. First of all your question, as it is with any subject related to comprehensive analysis, does not have any easy and short answer to it. However, I will try to address it in a simplified manner. Second, you should know that political entities are driven by logic and socio-economics no matter what their backgrounds or religions are and they are intertwined with multiple other political and social entities.

Although the fall of Constantinople is 1453, it is not the only siege on Constantinople done by newly expanding Ottoman Empire, in fact it is the third siege: First being 1394-1402 siege of Constantinople led by Bayezid I which was abandoned due to Timurid incursion into Anatolian territories, second being 1422 siege of Constantinople led by Murad II which resulted in a prolonged war and phyrric victory for Byzantine and third being the 1453 siege of Constantinople by Mehmed II.^(1) So I would argue that Ottomans did not ignored the Byzantine capital. An excerpt from The Cambridge History of Turkey Volume 1 may prove useful to your question regarding the "Were Christian western powers not concerned by this Muslim intrusion?": " During these desperate times, Manuel renewed his appeal to the west for help. He found a willing listener in King Sigismund, for with the conquest of Bulgaria, Hungary’s independence was also threatened by the Ottomans. Sigismund’s call for a crusade was answered by a number of European powers, particularly France. The venture ended in disaster at the battle of Nikopolis in 1396 ."^(2) Throughout Ottoman expansion into former Byzantine territories, Byzantine emperors plead for help on multiple occasions, however either they were not taken seriously, due to the tendencies of political entities being rational decision making instituties where immediate threats were substantially important than distant ones, or they were taken seriously however Ottoman forces become victorious over the collective crusader forces.^(3) About attempts to reconquer the lost territories, there are no attempts specifically made by Byzantine forces themselves since they were dealing with multiple civil wars (1321-1328 civil war, 1341-1354 civil war and 1380 civil war) through most of Ottoman conquests.

However from the formulation of the questions, one gather that there is a misinterperetation of history as Byzantine Empire was in fact only battling against the Ottomans in their latter years. However this assumption is incomplete, as all political entities think in terms of survival so did the Byzantine Empire and their relations with Ottoman Empire differed greatly from circumstance to circumstance and power configurations in Europe and Asia Minor. For example: Early Ottoman state formation were mercenaries for Byzantines, during the reign of Murad I 1362-1389 Byzantines were vassals of the Ottoman Empire and after Murad I they were once again enemies, which started the series of sieges on Constantinople.^(4) Also there are social, economical, cultural, political, and billion other factors that I did not had chance to touch upon which ultimately formulates a matrix where one can observe the different political entities and their interactions with one another. I highly recommend you to read The Cambridge History of Turkey Volume 1 Byzantium to Turkey 1071-1453 as it will answer all your questions regarding to Byzantine and Ottoman relations and more.

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1- See. The Cambridge History of Turkey Volume 1 Byzantium to Turkey 1071-1453 edited by Kate Fleet, (Cambridge: Cambridge University Press, 2009).

2- Ibid, pg.43.

3- See. Battle of Nicopolis or Crusade of Nicopolis.

4- Ibid, pg. 29-50.