T.C. Barnard 
The English Republic 1649-1660 [PDF ebook] 

The book begins by introducing the complicated events leading to the execution of Charles I in 1649 and then offers a detailed analysis of the political experimentation which followed. Toby Barnard argues that although the survival of the revolutionary order was bound up with Cromwell, and collapsed after his death, the regime defeated both its domestic and foreign enemies and was more stable than has often been thought. The book also investigates changes on the structures of power, on the ruling elites and in the localities.