Q: Context: The melting pot is a monocultural metaphor for a heterogeneous society becoming more homogeneous, the different elements "melting together" into a harmonious whole with a common culture or vice versa, for a homogeneous society becoming more heterogeneous through the influx of foreign elements with different cultural background with a potential creation of disharmony with the previous culture. Historically, it is often used to describe the assimilation of immigrants to the United States. The melting-together metaphor was in use by the 1780s. The exact term "melting pot" came into general usage in the United States after it was used as a metaphor describing a fusion of nationalities, cultures and ethnicities in the 1908 play of the same name.

Question: what process is the central idea behind americas melting pot? Let's give stream of consciousness first:
To answer this question, we should know that: Historically, it is often used to describe the assimilation of immigrants to the United States. Therefore, the final answer is assimilation.