The Jews of the Byzantine Empire were heavily persecuted, especially after Christianity was declared to be the official religion by Theodosius 11(408 – 450), who excluded Jews from the basic rights of citizenship and prohibited the building of new synagogues. His successor, Emperor Maurice, was even worse. He transformed all synagogues within his empire into churches and forcefully converted Jews to Christianity. The situation deteriorated even further as the Byzantine Empire declined.
When the Ottomans captured Bursa in 1324 , they found a Jewish community oppressed under Byzantine rule. The Jews welcomed the Ottomans as saviours. Sultan Orhan gave them permission to build the Etz ha-Hayyim (Tree of Life) synagogue which remained in service until 50 years ago.
Early in the 14th century, when the Ottomans had established their capital at Edirne, Jews from Europe, including Karaites, migrated there. Similarly, Jews expelled from Hungary in 1376, from France by Charles VI in September 1394, and from Sicily early in the 15th century found refuge in the Ottoman Empire.