>This got me thinking, is there a general pattern of physical conditions that have been or can be identified to where violent revolution becomes viable?
Absolutely, and the best tool to analyze this pattern is Gramsci's concept of Cultural Hegemony. One way in which Gramsci broke with previous Marxists is rejection of bourgeois rule as a "dictatorship" in the classic sense of the term. Rather he viewed their position as hegemonic, which is to say it was dominant (especially in proportion to its numbers), but that this dominance relied to a large degree on the acquiescence of other classes. Those groups which lived comfortably under bourgeois rule were content to perpetuate it, and with their support remaining dissident elements could be contained using relatively little open repression. If you want a quintessential example, the white working class in postwar America lived comfortably, and so they were content to allow the continued rule of the big bourgeoisie, and tolerated and even enthusiastically enforced the repression of Black America, which formed the principal basis for rejection of the ruling order. Not only this, but these middle classes, because they are sustained reasonably well by the status quo, can far more easily internalize bourgeois culture and ideology, and thus accept the myths and ideology of bourgeois society. Going back to my example, its why so many people who grew up in that time (ie boomers) believe in American bourgeois ideas (muh American dream muh bootstraps etc).
Revolutions happen when this hegemonic order begins to break down, and herein lies the source of the pattern you noticed. Uneven development is a core feature of capitalism, and the differing conditions in the first versus the third world cause these breakdowns to play out according to different patterns. The accumulation of wealth in the global north allows for the maintenance of a relatively large middle class, and thus a large population of people (including many workers) to be integrated into the bourgeois hegemony. The global south, as the target of imperialism and generally being poorer, cannot sustain such a middle class. Thus the hegemonic order in third world nations is inherently weaker, and they often find themselves in near-perpetual states of low level crises. The global north by contrast is only affected by major crises such as stock market crashes on the level of 1929 or 2009, as well as major wars (at least Vietnam tier or bigger).
This means that there are obviously more opportunities to make revolution in the global south, and that successful revolutions can often take a "slow burn" approach. It's why strategies like protracted people's war are so effective. In the developed world, these crises are typically far shorter and sharper, and thus revolutions follow patterns of rapid insurrection. The obvious example of this is the Russian vs the Chinese revolutions (yes Russia was still mainly feudal, but the revolution was still spearheaded by industrial labour). Thus a society's revolutionary potential is directly proportional to how capable it is of creating a large and comfortable middle class. What is encouraging today in the West is that capitalism seems to be entering a protracted state of global crisis, and it is less and less capable of sustaining such a class.