What is the purpose of beginning the text with an anecdote then moving to
the scientific and historical information?

Anecdotes help attract or hook the reader. The job of an anecdote is to interest the reader into looking further into your article.

the civil rights act was passed on april 9, 1866 by a republican dominated congress. it was passed over president johnson's veto, in an effort to push back against discrimination of african americans.

wheres the passage with the idiom underlined