Parliament passed the Self-denying Ordinance in April 1645, requiring most members of either House to resign military commands. The measure removed several aristocratic commanders and complemented the creation of the New Model Army. Cromwell was repeatedly exempted and retained his increasingly important command.

The ordinance encouraged a new rhetoric of public service, merit and self-sacrifice. It also weakened traditional assumptions that military command naturally belonged to noble birth, a social change reflected in radical army literature.