The title says it all. There's this notion in popular culture that Oliver Cromwell was a genocidal monster that tried to murder half the population of Ireland. This idea doesn't really stand up to even a cursory glance at the actual casualty figures or the events of the British Civil War(s). Cromwell's campaigns in Ireland, while admittedly bloody, were not substantially different from the conduct of similar Continental military leaders of the same era, like Albrecht von Wallenstein, Count Tilly, or Johann Baner. Additonally, Cromwell's campaign in Ireland only lasted a year or two in 1649-50. The English conquest and economic and political colonization Ireland was an ongoing process that began in Tudor times and continuned, arguably, right up into the 20th century. Pinning the full range of English misdeeds in Ireland, true or otherwise, on the personage of Oliver Cromwell, is to ignore the geopolitical interests and motivations of the English government both before and after the English Civil War.
While Cromwell may have been, even by the standards of his own time, a religious and political radical, I don't think claims by either English or Irish historians that paint Cromwell and the Puritans as a bunch of bigoted fanatics are really entirely fair. This isn't to say that the English Puritans weren't a bunch of religious whackos by modern standards, but to judge them that way ignores the political and cultural context in which they existed.
What's the consensus of scholarly historians, as distinct from popular culture? I have this argument nearly every year around St. Patrick's day.
TL;DR: Oliver Cromwell -- misguided radical, or histories greatest monster?
EDIT: Just to forestall any claims otherwise, I'm not saying that any of what Cromwell did was right by modern standards (it wasn't!) -- rather I'm making a plea to try to understand the past on it's own terms, rather than through the lens of modern nationalist rhetoric.
A follow-on question, if I may?
I have heard that Cromwell'd reconquest of Ireland was a last Death blow for the old Irish clan system (which had been under assault for a long time) and that in the fighting, most of the Irish elite or nobility was killed or exiled, meaning that English and protestant landowners replaced native Irish and catholic ones. Are there any thruth to this?
I would argue that it's a little bit of both. Clearly, the Cromwellian conquest was an incredibly bloody affair. When Drogheda fell, about 2800 soldiers died and 700-800 civilians. When Wexford fell, about 2000 soldiers were killed and 1500 civilians. Roughly 500 soldiers and 5000 civilians died at Limerick. As to the population drop, the estimates vary wildly. Some claim half of the population was executed. Podraig Lenihan's estimate of about 25% (Of a pre-war population of roughly 1,400,000) is probably the most accurate (mostly because while we do see severely diminished output, we don't see the societal collapse that would be expected from the higher figures).
Whether this was considerably crueler than the other wars of the day is a big question. In the 30 years war, at the sack of Magdeburg ended in the death of roughly 20,000 of its inhabitants. Now one big difference that's to be noted here is that at Magdeburg the executions were not supervised as the Cromwellian ones were, but were the result of an army allowed to run roughshod over a population. On the other hand, concept of murum ares attigit was practiced at the time. Meaning, that if a town resisted, once it fell the conqueror could do with the inhabitants as he pleases. Also, a notable concept of the time is that in order for a surrender to be valid, it must both be offered and accepted. This is how executions of prisoners such as occurred at the battle of Dungan Hill could happen. That being said, I am unaware of any of Cromwell's contemporaries that felt it necessary to order the slaughter of multiple towns and cities.
However, I don't think it was necessarily Cromwell's conduct in battle that earned him his reputation. In order to make it more difficult for gurrilla forces he instituted a policy of burning crops, which led to a famine, which accounted for the majority of the war's casualties. There's also the matter of land confiscation at the end of the war. Though Cromwell Act's plantation was neither the first nor last, it was the most severe. Catholic land ownership was reduced from 60% to 9%. Now it is certainly not the sole factor, but it was a major contributor to the potato famine. This is because the smaller amounts of land that was allowed to the population favored the potato, and the population had little to no say in where the food produced on plantation land went. This is why Ireland was still a major exporter of food during the famine. However, the act that probably sets Cromwell apart from his contemporaries was the rejuvenation and expansion of the indenture of Irish (which already existed, to a lesser degree). He send somewhere between 12,000 and 60,000 Irish into indenture in Barbados that were typically not prisoners of war, but rather those that took issue with the plantation.
Essentially, Cromwell probably was more cruel than his contemporaries. That being said, in the context of 17th century warfare, his actions were much more justifiable than they would be today.