Why did the roman emperor hadrian expel the jews from palestine?

Well, The Jews lived in Palestine as a nation under the rule of the Roman Empire until a revolt in A.D. 132 caused the Roman Emperor, Hadrian, to permanently expel the Jews.  

So, our answer would be:

"The Jews had started a revolt"

a) hostility to or prejudice against jews.

b) the holocaust, also referred to as the shoah, was a genocide during world war ii in which nazi germany, aided by its collaborators, systematically murdered approximately 6 million european jews             , around two-thirds of the jewish population of europe, between 1941 and 1945.