Disputing the sudden and devastating crash of the US stock market prices on the Black Tuesday, October 29, 1929 as the primary cause of The Great Depression of the twentieth century,
it has been claimed as the manifestation of a deeper malaise that plagued not only the US but also many other countries in the worldDispute and the claim was done by historians, so the non-underlined modifier should modify historians. Thus, A and B are eliminated right off the bat.(A)
it has been claimed as the manifestation of a deeper malaise that plagued not only the US but also many other countries in the world -- For reason mentioned above
(B)
it has been claimed as the manifestation of a deeper malaise that plagued not only the US but many other countries also in the world -- same as A
(C) Some noted historians of the day claimed it as the manifestation of a deeper malaise that plagued not only the US but also many other countries in the world
-- CORRECT modifier and simple past tense, since the timeframe is clear from the sentence.(D Some noted historians of the day
had claimed it as the manifestation of a deeper malaise that plagued not the US only but also many other countries in the world -- unnecessary past perfect tense
(E) Some noted historians of the day
claiming it as the manifestation of a deeper malaise plaguing not only the US but also including many other countries in the world -- This is a sentence fragment.
So, answer is
CP.S.: Edited formatting.