Final answer:
The resurgence of the Ku Klux Klan in the early 1900s was fueled by a romanticization of its past, racial and nativist ideologies, and a societal search for identity, which was influenced by the media and eugenicist pseudoscience.
Step-by-step explanation:
The Ku Klux Klan reemerged in the early 1900s primarily because some white southerners maintained a romantic view of the original KKK, and they sought to restore white supremacy in all facets of American life. The early 1900s resurgence of the KKK directly coincides with the release of D. W. Griffith's Birth of a Nation, a film glorifying the late nineteenth-century Klan. In addition, eugenicist ideas promoted by figures like Madison Grant, who suggested that immigration was contributing to the decline of the 'great race', stoked nativist sentiments among Americans.
Thus, evidence from the text suggests that the KKK reemerged due to a multitude of factors, including the perpetuation of white supremacist ideals, a sense of identity and belonging that the Klan provided to its members, and a nativist reaction to immigration and perceived racial dilution.