Why was the possibility of the Chinese entering into in the Korean War overlooked?

Your work must be 11-12 pages in length (not counting cover page, if used, and reference pages), and cited using Chicago style documentation. A minimum of five (5) sources are required, of which only one (1) may be an Internet source (general website). (A published source which is accessed in the online format such as the Military History Quarterly is not considered an online source.)