The Jews were hated in medieval times for the same reasons people hate banks and other money lenders now. People are happy to borrow money, they just resent having to pay it back! For centuries, the only group of people permitted to lend money were the Jews as moneylending for profit was seen as a sin against God. In the same way as there would be celebrations today if a bank burns down and loses all records of their debtors, societies were happy for the local Jews to be attacked for the same reason.
Secondly, Zionism led to much fear and hate, in Europe especially. Until the 19th century Jews had to live separately in ghettos, they weren't permitted to own property, businesses, enter professions etc. Then the European nations scrapped their anti-Jewish laws during the 19th century - Britain in 1869, France and Germany in 1870, Spain in 1898 etc. As soon as Jews were given equal rights many (Zionists) started pressuring European governments for their own land named Israel. Zionists didn't want Israel to be in some tropical hell hole - they demanded that one of the European powers give up land in Europe for Israel from which the residents would have to leave to make way for Jews. For example, Zionists suggested that Kent and Sussex become Israel if it were decided Israel be in the UK. Then all non-Jews would have to leave their homes and land as refugees. For several decades Europeans were terrified who would be expected to leave their homes and make way for Israel.
The issue became known across Europe as 'The Jewish Question' and for decades everyone was hoping for a 'Solution to the Jewish Question'. The whole thorny issue became a vote loser and something to be avoided (like racial issues today) and not talked about.
In Germany people were just as scared of Zionism. In 1932 Adolf Hitler was elected as he was the only politician prepared in that election to offer a 'Solution to the Jewish Question' - which was to bring back all the anti-Jewish laws Germany scrapped in 1870. Hitler was elected on that promise and that's what the Nazis did during the 1930s. Then it was decided at the secret conference at Wansee in 1942 that there had to be a 'Final Solution to the Jewish Question' - that all Europe's Jews had to die. That became known more simply as 'The Final Solution'. After the war the UK granted Jews their mandated territory of Palestine as Israel - with all that entails to this day. It was the Palestinians had to leave their land, businesses and homes as refugees and many are still in those refugee camps today.
Jews were hated for two main reasons - they were money lenders and then there was Zionism which terrified everyone.
The same hatred persists today - especially amongst Muslims. My Muslim neighbour gets quite tiresome as he tells me that Jews aren't human and he continually blames them for the world's woes. He says Jews run the US and Europe, he blames them for the wars, the economic mess of the EU etc. Every topic seems to be turned around to the Jews and I get bored with it. However, he's not alone. I haven't met a Muslim yet who liked Jews and Israel is surrounded by enemies.