During Ottoman rule, from the late 15th through the early 20th century, Jerusalem had either a Jewish plurality or an outright Jewish majority. In 1854 Karl Marx was a reporter for the New York Daily Tribune. His article of 15 April 1854 reported the population as follows:
What made east Jerusalem Arab? 19 years of illegal Jordanian occupation ending in 1967. In 1948 when Jordan captured the old, walled city they destroyed 58 synagogues. 58! I somehow don't think Arabs were worshiping in those synagogues. Yep, in 1948 there were still lots of Jews in "Arab East Jerusalem".
Here is a description of how Jerusalem was divided until the Six Day War written by former Israeli President Chaim Herzog in his 1982 book The Arab-Israeli Wars:
Mount Scopus [was] an Israeli enclave on the site of Hebrew University and Hadassah Hospital; it had been completely surrounded in 1948, but held out against all Arab attacks. The second enclave was Government House, which had been the residence of the British High Commissioner of Palestine...
Yes, the majority of the eastern part of the city today is Arab. That's true, in part, because Jerusalem has grown and swallowed up several Arab villages and, in part, through natural population growth in the Arab community. There are also a number of Jewish neighborhoods in the eastern part of the city.
It may be possible, someday, after a period of peace, to separate Arab areas that aren't part of the historical city and place them under Arab rule. Right now, though, I don't see this is practical. I do not support dividing the city again and I do not accept the idea that any part of Jerusalem is intrinsically Arab and must be ceded.
If you, like I, support keeping Jerusalem united you may wish to visit OneJerusalem.org. Tomorrow is the 40th anniversary of the reunification of Jerusalem. To me, that is something to celebrate and cherish.