Fourth Crusade and sack of Constantinople

The sack of Constantinople occurred in April 1204 and marked the culmination of the Fourth Crusade. Crusaders sacked and destroyed most of Constantinople, the capital of the Byzantine Empire. After the capture of the city, the Latin Empire (known to the Byzantines as the Frankokratia, or the Latin occupation) was established and Baldwin IX of Flanders crowned emperor in Hagia Sophia.

After the city's sacking, most of the Byzantine Empire's territories were divided up among the Crusaders. Byzantine aristocrats also established a number of small independent splinter states—one of them being the Empire of Nicaea, which eventually recaptured Constantinople in 1261 and proclaimed the reinstatement of the Empire. However, the restored Empire never managed to reclaim all its former territory or attain its earlier economic strength, and it gradually succumbed to the rising Ottoman Empire over the following two centuries.

The Byzantine Empire was left poorer, smaller, and ultimately less able to defend itself against the Seljuk and Ottoman conquests that followed. The actions of the Crusaders, therefore, accelerated the collapse of Christendom in the east, and in the long run helped facilitate the later Ottoman conquests of southeastern Europe.

The sack of Constantinople is considered a turning point in medieval history. Reports of Crusader looting and brutality horrified the Orthodox world; relations between the Catholic and Orthodox churches were wounded for many centuries afterwards.