(out)Here are some sources explaining why the concept of American conservatism is problematic: 
 *Political ideology today (2001), Ian Adams, p. 32:  "Ideologically, all US parties are liberal and always have been." 

 *"Why I am not a conservative" (1960), F. Hayek:  "what in Europe was called "liberalism" was here the common tradition on which the American polity had been built: thus the defender of the American tradition was a liberal in the European sense.[2] This already existing confusion was made worse by the recent attempt to transplant to America the European type of conservatism, which, being alien to the American tradition, has acquired a somewhat odd character."  [Footnote:  2. B. Crick, "The Strange Quest for an American Conservatism," Review of Politics, XVII (1955), 365, says rightly that "the normal American who calls himself 'A Conservative' is, in fact, a liberal." It would appear that the reluctance of these conservatives to call themselves by the more appropriate name dates only from its abuse during the New Deal era. 

 *Conservative parties and right-wing politics in North America (2003), Rainerp-Olaf Schultze and others, p. 15:  Because of these divergent backgrounds, the term "conservatism" came to acquire a different meaning in both countries.  Rather than to European notions of conservatism, the American version relates to classical liberalism.  George Grant, a prominent Canadian conservative intellectual, has contended that: 
 :"Americans who call themselves 'conservatives' have the right to that title only in a particular sense.  [...]  Their concentration on freedom of governmental interference has more to do with nineteenth century liberalism than with traditional conservatism, which asserts the right of the community to restrain freedom in the name of the common good." 

 *Conservatism in America (2007), Paul Gottfried, p. 2:  "In this book, I intend to investigate another equally blatant mislabeling, one that pertains to American "conservatives"." 

 You really have to define the subject in the lead to explain why you are including US conservatives.