Crusade of Nicopolis in the context of "Crusade of Varna"

The Ottoman–Venetian wars were a series of conflicts between the Ottoman Empire and the Republic of Venice that started in 1396 and lasted until 1718. It included:

• Venice's participation in the Crusade of Nicopolis in 1396
• A naval conflict in 1415–1419, the main event of which was the Battle of Gallipoli (1416)
• The Siege of Thessalonica (1422–1430), with Venice active from 1423 on, resulting in the capture of Thessalonica by the Ottomans
• The First Ottoman–Venetian War (1463–1479), resulting in the capture of Negroponte, Lemnos and Albania Veneta by the Ottomans
• The Second Ottoman–Venetian War (1499–1503), resulting in the capture of the Venetian strongholds in the Morea (Peloponnese) by the Ottomans
• The Third Ottoman–Venetian War (1537–1540), resulting in the capture of the Cyclades except Tinos, the Sporades and the last Venetian strongholds in the Morea (Peloponnese) by the Ottomans
• The Fourth Ottoman–Venetian War (1570–1573), resulting in the capture of Cyprus by the Ottomans, and the defeat of their fleet in the Battle of Lepanto (1571)
• The Fifth Ottoman–Venetian War or the Cretan War (1645–1669), resulting in the capture of Crete by the Ottomans
• The Sixth Ottoman–Venetian War or the Morean War (1684–1699), resulting in the capture of the Morea (Peloponnese), Lefkada, Aigina and parts of Dalmatia by Venice and the end of Ottoman dominance in the eastern Mediterranean Sea
• The Seventh and last Ottoman–Venetian War (1714–1718) (also called the Second Morean War or Sinj war), resulting in the recapture of the Morea (Peloponnese) and of Tinos and Aigina, the last Venetian holdings in the Aegean, by the Ottomans

The siege of Constantinople in 1394–1402 was a long blockade of the capital of the Byzantine Empire by the Ottoman Sultan Bayezid I. Already in 1391, the rapid Ottoman conquests in the Balkans had cut off the city from its hinterland. After constructing the fortress of Anadoluhisarı to control the Bosporus strait, Bayezid tried to starve the city into submission by blockading it both by land and, less effectively, by sea.

The Crusade of Nicopolis was launched to relieve the city, but it was decisively defeated by the Ottomans. In 1399, a French expeditionary force under Marshal de Boucicaut arrived, but was unable to achieve much. The situation became so dire that in December 1399 the Byzantine emperor, Manuel II Palaiologos, left the city to tour the courts of Western Europe in a desperate attempt to secure military aid. The emperor was welcomed with honours, but secured no definite pledges of support. The city was relieved when Bayezid had to confront the invasion of Timur in 1402. Bayezid's defeat in the Battle of Ankara in 1402 and the subsequent Ottoman civil war enabled the Byzantines to regain some lost territories in the Treaty of Gallipoli.