In the timeline, Constantinople never fell to the Ottomans, and became an independent city-state, and later nation-state. In the ATL, the Black Death never reached the city, and a different, less expierenced Ottoman general invaded. Although the city was damaged, the local government (in the absence of the dead Byzantine monarch) negotiated a peace treaty. Constantinople would run its own affairs without fear of further Ottoman military aggravation, but the new country would allow the empire open borders. The Byzantine empire collapsed only days later, leaving the economic powerhouse of the Kingdom of Constantinople in its wake.