"Biggest Evacuation" since the Civil War

NBC news keeps saying this about the Southern California fires. First, they kept throwing out the figure of about 1 million...while others say 500,000.

In any case, while there's no doubt there were civilian evacuations during the American Civil War, I can't think of any evacuation that came close to 500,000 people over a short-period of time (if it's longer I'd call it a "migration"), let alone 1 million during the American Civil War [proportionally "maybe" as there were only about 30 million or so people in the country).

Can anyone else?