King realized white America was not ready for racial equality.

Evidence

Barely removed from the euphoria of the 1963 March on Washington and his historic “I Have a Dream” speech, and the legislative triumphs of the Civil Rights Act of 1964 and the Voting Rights Act of 1965, Dr. King now confronted the uncertainty of his moral vision for the country. White America was not ready for racial equality. The violence against peaceful demonstrators marching for open and fair housing in Cicero, Illinois, a racist white suburb outside of Chicago, had made plain (though King knew this already) that racism was not a unique disease of the South. The hatred was clear, and it was American. — Eddie S. Glaude Jr., Democracy in Black, 259