Why was constantinople an important city?

  It is an important trade center due to its location. Ever since the days of human expansion from Southwest Asia to Europe, people needed a way to cross the Bosporus strait that separates Anatolia from the Balkan Peninsula. The Bosporus is also the only water passage between the Mediterranean and the Black Sea. Whoever controlled this location controlled (and profited from) both land and water transportation in the area. Silk Road trade brought east and west together at Constantinople, and the Crusades exposed otherwise European-minded soldiers to the world beyond their own continent, further increasing the city's importance. Renaissance innovations made ocean travel possible, allowing western European countries to navigate around Africa on their way to Asia, bypassing the "choke point" at Constantinople and reducing its importance as THE global center of trade. However, it still remains a cultural and economic crossroads between East and West. Because it gave the Ottomans access to other trade routes. 

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