Page 618 of Zinn:

"It turns out (and we have the experience of all bourgeois, socialist and national revolutions to support this) that no form of government, once in power, can be trusted to limit its own ambition, to extend freedom and to wither away. This means that it is up to the citizenry, those outside of power, to engage in permanent combat with the state, short of violent, escalatory revolution, but beyond the gentility of the ballot-box, to insure justice, freedom and well being, all those values which virtually the entire world has come to believe in."