I'm almost finished reading The English Republic 1649-1660 by Toby Barnard, and it struck me that a few of the attempts to build a working government seemed to be somewhat similar to the balance of powers seen in the American constitution.

Of course, it wasn't truly balanced, since Cromwell always had most of the power. But it seemed interesting to me that what I know of the later Constitution almost seemed like an edited version of the Instrument of Government, in the sense that powers were shared between the Lord Protector, Parliament, and the Council of State.