Ford's antisemitism is well documented and there is another AskHistory thread with a decent answer to a similar question.

I would argue that Ford's antisemitism and notorious belief in conspiracy theories are interrelated and fed each other. As for which came first? I don't think there is an answer for that particular question that I am aware of.

After the publishing of some negative stories in the Chicago Tribune in 1919, Ford sued the paper for libel. In that court case he was deposed and his testimony is one the possible origination of his famous quote "History is bunk." while the transcript never puts those words in that order, it does appear that Ford believed that history was less about the facts of the past and more about perceptions and power.

After losing the case, he acquired the Dearborn Independent, a struggling newspaper local newspaper to his factories, he placed one of his lieutenants E.G. Liebold in charge of the paper and closely supervised the stories and reporting that it printed. One of the series the paper published was "The International Jew" which attempted to prove that a conspiracy theory that a international cabal of Jewish financiers and bankers controlled politics and history. The publication of this series was influential in the dissemination of antisemitic ideologies throughout its time in print. The series would published the Protocols of Zion, which remain one of the most influential pieces of antisemitic writings, and other stories.

Ford was incredibly interested in proving his vision of history and printed many associated stories including some rather strange tales. Ford at one point picked a book called The Escape and Suicide of John Wilkes Booth by Finis Bates (1907) which he found fascinating. Bates alleged he had met John Wilkes Booth in Texas long after his official death in 1865 shortly after the assassination of President Lincoln. Bates would eventually become the owner of a mummified corpse which he claimed proved Booth lived for years after the fact and would appear often at sideshows and carnivals around the country. Bates argued that Booth's survival was possible due to the fact that he was in league with Vice President Andrew Johnson who had "conspired" to kill Lincoln in order to become president himself and cover up the fact that Booth had survived.

Ford was intrigued with the story and believed that the conspiracy to kill Lincoln extended beyond Johnson and was done in part because Lincoln had implemented a monetary policy that had angered Jewish Canadian bankers. So Ford connected the dots. Needless to say, while the Booth conspiracy Bates laid out, and the many other versions, were never proven or provide any reasonable evidence, Ford ended up printing the story in "the International Jew" as another example of how Jewish Bankers dominated history.

There have been many serious historical studies of antisemitic thought and its origins but in Ford's case, it appears that his antisemitism developed a long side his other conspiratorial ways of thinking. However there is very little about his antisemitism that is unique, Ford simply had the wealth and capabilities to spread his ideas but many others shared them. Other prominent figures shared similar view points. A few years after Ford shut down the Independent and made a public apology about his antisemitic politics a Catholic priest a few miles away in Royal Oak, MI at the National Shrine of the Little Flower began broadcasting a well-known radio show. Father Coughlin would deliver tirades against Jewish bankers throughout the 30s and became a vocal supporter of fascism. So Henry Ford cannot be considered the only figure participating in antisemitic propaganda and both Ford and Coughlin hint at a larger supportive audience of Americans who shared their antisemitic views.

Sources:

Max Wallace. The American Axis: Henry Ford, Charles Lindbergh and the Rise of the Third Reich. New York: St. Martin's Press, 2003.

Ford R. Bryan: Henry's Lieutenants. Detroit, Mich.: Wayne State University Press, 1993.

Evans, C. Wyatt. The Legend of John Wilkes Booth: Myth, Memory, and a Mummy. University Press of Kansas, 2004.

Warren, Donald. Radio Priest: Charles Coughlin The Father of Hate Radio. New York: The Free Press, 1996.

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