The first thing to know is that in all societies, there are ‘scapegoats’, people who are singled out for no other reason than their being different (in religion, in skin color, in language, or sometimes even less than that) and who are used by the majority of the population to vent their anger and their fear at. It’s awful but happens all of the time.
Historically, the roots of antisemitism can be found between the last days of the Roman Empire and the Early Middle Age in Europe. Christianism was converting all of society and progressively removed all so-called ‘pagan’ beliefs. However, its relationship was more uneasy. Judaism was the matrix of Christianism and both have a number of sacred texts in common. Jesus was Jewish. Christianism was ruthless with other religions, but with judaism it did alternate between toleration, protection and repression. Some priests and popes would protect them, others would try to eradicate them.
In the 19th century, a century of deep social, political and economic changes in Europe, Jews started to enjoy equal rights in Europe, thanks to the Enlightenment, the efforts of people like Moses Mendelssohn and the ideals of the French Revolution spreading around Europe. However, at the same time, there was a strong reactionary movement against modernity. And for many of them, Jews proved a convenient scapegoat. Jews were associated with many of the powerful forces: democracy, equal rights, finance, intellectuals, etc. Conspiracy theories rose, and some found them convenient to use. The most infamous example of this is the invention of the Protocols of Zion.. These were forged by the Russian secret police, the Ochrana, in order to direct popular anger in Russia from the tsarist regime to the Jews. This movement continued and culminated into nazism, where Jews became a scapegoat for the German defeat in World War I and the economic crises in the 1920s and 1930s. After World War II, European countries made unprecedented efforts to root out antisemitism, with significant success. But there was just too much antisemitism – old books, old theories, and old lies to be entirely removed.
In 1948, Israel gained independance after a long struggle from the Zionist movement. But the independance of Israel and the conflict between Israelis and Palestinians created a new ground for antisemitism. If we put aside the Palestinian liberation movement, its direct motivations and the reactions of the Israeli authorities (since this is a heated and important debate by itself), it can be argued that Israel and Jews have since then been seen in Muslim countries as Western countries, and Jews have become again a scapegoat for all the tragedies that happened in the muslim world since then.
Without entering into too much detail, the tragedies of muslim people can be assigned equally to the consequences of European and American imperialism, and to the corruption and incompetence of local elites who would rather blame foreigners than accept any criticism of their rule. Back in Europe, a new kind of antisemitism has spread among populations coming from muslim countries, where the difficulties of integration have led a noisy minority to turn to antisemitism.
As noted, there is no antisemitism in China, India, Japan. But it has spread among Christian and then Muslim countries; and since this represents the majority of the world population, there is unfortunately some truth to the assertion that ‘everybody hates Jews’.