but the main people were not Jewish at all

Actually a large number of very prominent Bolshevik leaders were Jewish, it's just that they begin to be forgotten since so many of them were purged by Stalin in the 1930s, they include:

Leon Trotsky Grigory Zinoviev Lev Kamenev Yakov Sverdlov Moisei Uritsky Yakov Sverdlov Grigori Sokolnikov

Later on, Lazar Kagnovich was a prominent Jews in Stalin's inner circle, Molotov's wife Polina was also Jewish.

Most of those people in the above list held politburo seats (A very small committee of 5-8 full members and maybe a dozen candidate members which was the highest level of political decision maker in the USSR) despite the fact that Jews were a very small percentage of the population in the USSR.

At one point Trotsky, Zinoviev, Kamnev were full Politburo members together, meaning 3 of the 5 most powerful political figures in the Soviet Union were Jewish (the other non-Jewish 2 politburo members were Lenin and Stalin) despite being an extremely small part of the overall population. This situation was not to last of course, but it does indicate a disproportionate Jewish membership in the Communist leadership in its early years.

Hatred doesn't always have to be rational or fully rational. There was many Jewish folks in the leadership of the Bolsheviks Trotsky and Grigory Zinoviev being the highest in leadership.

Because of the extensive persecution Jews faced in Tsarist Russia it many advocated for change within Russia or just left all together. Pogroms (forced death marches) were common.

Not to mention that Hitler later on spent extensive energy ensuring a clear ideological difference between Marxist socialism and Nazism. One of the crux's of this was of course linking communism with European Jews.

There was a strong socialist current in Germany before , during, after World War 1. One of the ideological leaders of a failed revolution was a Jewish Atheist, her name was Rosa Luxemburg.

With such strong antisemitism pervasive throughout Europe it becomes easy for politicians and political leaders to exploit primal fear and hatred to turn the working class against their own interests.

It's analogous to the Republicans getting poor whites to vote against their own material interests in the US through exploiting deeply held racist beliefs.

In Russia and the rest of Eastern Europe, Jews had good reason to oppose the aristocracy, with communism being the most viable alternative. In the rest of the world, Jews had similar reasons to dislike the unofficial aristocracies that held them out of much of society (for one obvious example, note all the hospitals out there with Hebrew names, which were founded because other hospitals wouldn't accept Jewish physicians), and the two movements that were working for change were the socialists and the fascists, and the latter held racism as a core tenet. In the US, the non-Marxist socialist wing of the Democratic party was popular.

Beyond that, Jews have long tended to be politically liberal (with some anthropologists doing research when I was in college positing a higher level of communality/lower level of individualism than other western cultures). In the US, this could be partly attributed to the centers of the Jewish population being in the northeast, but it may also be that economic regulation is an old part of Jewish community life while official social regulation was often something the Christian majority imposed on the Jewish minority.

Either way, most Jews today will be able to point to at least one grandparent or great-grandparent who was in a socialist movement.

I've actually made a post about this before on the /r/DebateFascism subreddit. So basically I'll give a brief explanation and then put up the original post which will really just repeat everything more in depth.

To understand the Jewish Communism belief that the National Socialists have, you have to look at what constituted a Jew. National Socialists (And a disconcerting number of Europeans in general) held the belief that Jewishness was more than the religion, but also the ethnicity. Therefore when someone says "Oh well Marx was secular!" they don't understand. Just by being born of Jewish blood, Karl Marx is a Jew for life in their view. So when you look at Communism, Jewish people (by the definition of the National Socialists) are very much represented. I'm not 100% sure why this is but I've read in the past that it likely has to do with the way the Russian government treated the Jews of Eastern Europe. Don't take my word for that though.

Anyway, that's the general gist of it. I'll just put the older post I made in a quote block if you want to read the whole thing. Direct link to my post here.

You have to understand the way people thought of Jews back then. For them, Jewishness was passed via genes. If your father was a Jew and mother a Gentile, then you were a half Jew. If your mother and father were Jews, then you were full Jewish. It's a fairly simple concept, just think of fractions lol.

After WW1, Communists were in full force. Not just in Russia but all around Europe, and most importantly, in Germany. There was a communist revolution in Germany to overthrow the government which started before the first world war was even over. This would later help contribute to the "stab in the back" theory because no land in Germany was over occupied by the Triple Entente and Germany (by their view) was largely brought down by the Jewish Communists who started the revolution.

It is also important to note that most of the head Communists of the groups that took place in the revolution were almost all ethnically Jewish, as in they had Jewish parents. Here are the largest names in the German Revolution.

Rosa Luxemburg, Jew

Kurt Eisner, Jew

Karl Radek, Jew

Leo Jogiches, Jew

Karl Liebknecht, Gentile

Clara Zetkin, Gentile

Ernst Toller, Jew

Gustav Landauer, Jew

Eugen Leviné, Jew

Paul Levi, Jew

Hitler likely would have witnessed this revolution himself and would have been in direct opposition with the Marxists. The revolution was put down almost entirely by Freikorps who were made up of German Veterans of the first world war. While Hitler did not serve in the Freikorps, many notable National Socialists did. Hitler and most of Germany was against Marxism after that.

In fact, you can see that many communist groups at that time period (even in the beginning) were ethnically Jewish.

Karl Marx, Jew

Friedrich Engels, Gentile

Vladimir Lenin, Jew

Leon Trotsky, Jew

However this was only an agitating agent for anti-semitism as if had existed in Western Civilization with the crucifixion. Christians never forgave that and naturally had a negative view of Jews. On top of that, Jew had a hard time integrating into other cultures and refused to do so in many cases (how do you think the Jews survived without a state for so long?). So anti-semitism was something rather prevalent in all of European Society, to claim otherwise would be untruthful.

On another front, Jews were very much over represented in things like investment banking. Naturally Hitler did not like these guys either and blamed the stab in the back and the economic collapse as well. I'm not too read on this particular piece of the puzzle but I do know that there were many Jews in investment banking. How much they dominated or if that was 100% logical is unknown to me. I'm not sure.

This is pretty much the logical way to explain the dislike of Jews in Germany. Granted, you have to look using Hitler's POV but I think it is relatively logical from that view.

On you final point, I have no clue about anti-semitism today. It's not something I have read much on. Hopefully someone else can answer your question on that.

Apologies for any spelling/grammar errors. I'm way to tired to actually re-read this thing right now.

Alright, so that was that. Now I'm no academic on the subject, so if anything is wrong, apologies ahead of time.

EDIT: Added a link to my post.

For some conservative anti-semites both capitalism and communism were outward manifestations of atheist modernism which was the key Jewish conspiracy. This was especially common among Catholic anti-semites of the 1920s and 1930s. I did some research on Fr. Denis Fahey, an Irish priest who influenced the American radio priest Fr Coughlan. He copied his ideas from France. In his view, the capitalists promoted Jewish interests from above and the communists did so from below.

Worryingly Fahey's writings are widely available on the Internet from various oddball reactionary Catholic groups.

Denis Fahey, The rulers of Russia (1938)