the Jewish community has been consistently demonised by regimes and forced them from their countries. What was the original cause for history's repeated anti-semitism?
Typically, it has come down to a few things:
Frequent minority status - Jews have, for most of history, been a minority in every area around the world. As such, it is rather easy to persecute said Jews, because they are unable to congregate in such a way that they can fight back. Minority groups that are easy to pick on, usually are picked on.
They are different, which is a rather clear-cut argument. Groups which stand out have commonly been persecuted, because they provide a convenient "Other" that can be used as a scapegoat for problems.
The biggest point has been the degree to which one stands out, I'd argue, and the prosperity of Jews in the areas they are later persecuted in. I believe that Theodor Herzl, the founder of political Zionism (the movement to establish a Jewish state), wrote it best in his pamphlet Der Judenstaat (The Jewish State, written in 1896):
...Modern Anti-Semitism is not to be confounded with the religious persecution of the Jews of former times. It does occasionally take a religious bias in some countries, but the main current of the aggressive movement has now changed. In the principal countries where Anti-Semitism prevails, it does so as a result of the emancipation of the Jews. When civilized nations awoke to the inhumanity of discriminatory legislation and enfranchised us, our enfranchisement came too late. It was no longer possible to remove our disabilities in our old homes. For we had, curiously enough, developed while in the Ghetto into a bourgeois people, and we stepped out of it only to enter into fierce competition with the middle classes. Hence, our emancipation set us suddenly within this middle-class circle, where we have a double pressure to sustain, from within and from without. The Christian bourgeoisie would not be unwilling to cast us as a sacrifice to Socialism, though that would not greatly improve matters.
...Anti-Semitism increases day by day and hour by hour among the nations; indeed, it is bound to increase, because the causes of its growth continue to exist and cannot be removed. Its remote cause is our loss of the power of assimilation during the Middle Ages; its immediate cause is our excessive production of mediocre intellects, who cannot find an outlet downwards or upwards—that is to say, no wholesome outlet in either direction. When we sink, we become a revolutionary proletariat, the subordinate officers of all revolutionary parties; and at the same time, when we rise, there rises also our terrible power of the purse.
...The Jewish question still exists. It would be foolish to deny it. It is a remnant of the Middle Ages, which civilized nations do not even yet seem able to shake off, try as they will. They certainly showed a generous desire to do so when they emancipated us. The Jewish question exists wherever Jews live in perceptible numbers. Where it does not exist, it is carried by Jews in the course of their migrations. We naturally move to those places where we are not persecuted, and there our presence produces persecution. This is the case in every country, and will remain so, even in those highly civilized—for instance, France—until the Jewish question finds a solution on a political basis. The unfortunate Jews are now carrying the seeds of Anti-Semitism into England; they have already introduced it into America.
...I believe that I understand Anti-Semitism, which is really a highly complex movement. I consider it from a Jewish standpoint, yet without fear or hatred. I believe that I can see what elements there are in it of vulgar sport, of common trade jealousy, of inherited prejudice, of religious intolerance, and also of pretended self-defence. I think the Jewish question is no more a social than a religious one, notwithstanding that it sometimes takes these and other forms. It is a national question, which can only be solved by making it a political world-question to be discussed and settled by the civilized nations of the world in council.
I quoted a few selected paragraphs that I think summarize it well, but if you'd like to read more, feel free to check it out (with an introduction/biography) on Project Gutenberg.
It has commonly and prominently been referred to as "The Jewish Question", and the discussion around it continued even after the founding of Israel. There is no question, however, that Israel has provided a "way out" for persecuted Jews in various countries, as per the many operations Israel has undertaken to rescue and extract Jews from conflict zones (Operation Magic Carpet from Yemen, for example). Despite violence surrounding Israel, it has often been considered a fallback option, and its advanced economy has afforded opportunity for immigrants as diverse as Soviet immigrants and African Jews (though not always with equal opportunity to all, as in most nations).
These are only a few factors which are commonly pointed out, but I think they're a good place to get the discussion rolling with further questions if anyone has them.
The short answer is that they were outsiders to many (mainly Christian) circles like in feudal times, and they "always" had gold and riches from banking and other jobs. Some bishops and others accused some Jews of witchcraft, poisoning wells, etc. and many peasants started attacking the Jews during crop failures (They "cursed" the fields) and the oppression continued because they were never accepted anywhere in the region.
The odd man out here is Poland, which accepted many jews during the Spanish Inquisition and other times with there lax religious laws.