Final answer:
The immediate outcome of the English Civil War was the triumph of Oliver Cromwell's Parliamentary forces, leading to the execution of Charles I and the establishment of the Commonwealth with Cromwell as its head, until the Restoration of Charles II in 1660.
Step-by-step explanation:
The immediate outcome of the English Civil War was the victory of the Parliamentary forces, known as the Roundheads, over the Royalist forces.
After sustained conflict from 1642 to 1649, which saw the New Model Army led by Oliver Cromwell achieve decisive victories, King Charles I was captured, tried for treason, and executed in 1649.
Subsequently, the monarchy was abolished and England was declared a republic, named the Commonwealth, with Oliver Cromwell at its head, serving in the capacity of a military dictator until his death in 1658.
The republican experiment ended in 1660 when Charles II was invited to return from exile and restore the monarchy, an event known as the Restoration.