Hmm...if Cromwell hadn't been such a puritanical jackass, do you think England might have completely dispensed with the monarchy for good?
I suppose it comes under the heading "jackass", but since Cromwell didn't groom a successor and ensure that the successor would have a smooth transition to power, then what happened was inevitable.
If he had ensured a successor, then what you have is just another form of monarchy, really.
The Royal family took power (8th century or thereabouts) as a military dictatorship. The King was essentially the owner of the entire country, and everyone else was his tenant. He "allowed" sections to various nobles who supported him. These were areas that they controlled anyway, but they kept control at the King's whim.
Kings and Nobles at that time, and for much of history were comparable to biker gangs or Mafia. They had the arms, they controlled territory, they collected protection money, extortion, loan sharking, etc. There's nothing new in all this we have today. The difference was, there was no one else claiming to be the government.
Wars were fought over territory and the winner owned the land and the people on it.
Since that time they've become marginally more civilized about it, but it all goes back to land that was siezed by force, political control over that land, and then passing that land on to their decendants. Titles are passed on to decendants, or bought and sold, or traded through arranged marriages.
The rise of first the craft guilds, and then the merchant houses meant that money (which was power) was shifting from land owners (nobles) to a new economic class. At first they could be bullied, then they hired their own security, built their own walls around their cities and bribed the men at the top. Eventually they wanted actual say in goverment, so the demanded a house of commoners to act alongside the house of lords.
Cromwell wasn't a democrat, he was just another power grabber who happend to be a commoner and made use of the existing parliament. I'll give him some credit for ignorance, he was living in a world where he had no example of democracy , so he had to make it up as he went along.