You are probably thinking about Ireland. Antonia Fraser's biography covers this in detail. Many things that happened under Cromwell's command were standard practice in siege warfare at the time. Of course, by modern standards it's atrocious, but that tells us more about the 17th century than about his personality. He also believed, rightly or wrongly, that he was responding to Irish atrocities against English settlers.
>Many things that happened under Cromwell's command were standard practice in siege warfare at the time.
I've seen other people argue this, but that statement is mostly the result of a single (self-proclaimed) amateur historian named Tom Reilly.
What he is saying is that it was the norm at the time to behead surrendered troops and put their heads on pikes around the area.
There's one real problem, though. That wasn't the norm at the time. It's never been the standard practice in siege warfare, especially in an attempted conquest, because it is stupid to do and discourages surrender later.
In fact, in other instances Cromwell himself accepted surrenders. So it wasn't standard at all.
In the end, though, whether or not Cromwell personally massacred thousands of civilians, he set up a government in Ireland and empowered the people that ended up causing the deaths of hundreds of thousands.
Here's a not-amateur historian who makes a similar argument:
Ó Siochrú, M., 2007. Atrocity, codes of conduct and the Irish in the British Civil wars 1641–1653. Past and Present, 195(1), pp.55-86.
Relevant quote: "This savage action [Drogheda] shocked opinion in Ireland and abroad, but by a strict interpretation of the rules of war Cromwell acted entirely within his rights. The commander of Drogheda, Sir Arthur Aston, refused a summons to surrender, thereby forfeiting his life and that of the garrison in the event of a successful assault."
Later he describes Cromwell as moderating his tactics in response to "facts on the ground": exchanging prisoners, and accepting the surrender of Clonmel. After Cromwell left Ireland, the war became bloodier.
Note that Ó Siochrú does not in general spare the English. He describes the "savage practices of England and Scotland" affecting Ireland in the 1640s, and gives examples of Irish prisoners of war being killed (in England), and of this being protested against by contemporary Royalists.
There's a huge difference between 'standard practice' and 'technically within your rights.' If it were standard practice, there would be no shocked opinion in Ireland and abroad.
Were there towns which refused to surrender? Colchester, when it finally surrendered during the second civil war, had to pay a ransom of £14,000 in exchange for not being pillaged, and the leaders of the defence were executed.
