Given the task definition and input, reply with output. In this task, you are given a question and a context passage. You have to answer the question based on the given passage.

Why do so few Americans view themselves as having descended from more than one ethnic group?, Context: The American people are mostly multi-ethnic descendants of various culturally distinct immigrant groups, many of which have now developed nations. Some consider themselves multiracial, while acknowledging race as a social construct. Creolization, assimilation and integration have been continuing processes. The African-American Civil Rights Movement (1955–1968) and other social movements since the mid-twentieth century worked to achieve social justice and equal enforcement of civil rights under the constitution for all ethnicities. In the 2000s, less than 5% of the population identified as multiracial. In many instances, mixed racial ancestry is so far back in an individual's family history (for instance, before the Civil War or earlier), that it does not affect more recent ethnic and cultural identification.
mixed racial ancestry is so far back in an individual's family history (for instance, before the Civil War or earlier), that it does not affect more recent ethnic and cultural identification