The Break-out was the mass migration of humans across interstellar space that began in the closing years of the 21st century.
The Break-out was covered in Break-out to Empire: Essays on the Third Millennium, edited and published by Galactic Federation Archivist Ven Kalik. (PROSE: Prelude Deceit)
A much larger Break-out, the Great Breakout, occurred in 5000. (TV: The Invisible Enemy)