By request, here's the shorter version of "What Helped the Voiceless? Historical Case Studies" as its own post. I've edited for coherence as a stand-alone post and for conciseness. My hope is that people feel free to share their thoughts on this, even if they haven't read the full report.

Key Takeaways:

I read about the histories of various policy shifts that benefited groups whose conditions limited their capacities for self-advocacy, especially abolition and economic expansions of voting rights. My main takeaways were: 

• These inclusive shifts were driven to a large degree by the influence of excluded groups, so it's a mistake to conclude from them that expanding circles of caring will eventually bring about good policies for groups that can't exert influence.
• Inclusive/exclusive political shifts usually happened because powerful groups were incentivized to make them happen.
  • [Edit 1/24/21: this comment from weeatquince suggests another approach along these lines: focusing more on increasing policy makers' consideration of the long-term interests of current generations, because there is much overlap between these interests and the foreseeable interests of future generations.]

Other takeaways:

• The timing of these modern era increases in inclusion can be largely explained through the impacts of industrialization: making excluded groups more able to resist exclusion, while making conflict more costly for elites.
• Takeaways for political strategy:
  • Look for versions of policies that are politically strategic to advocate, e.g. a policy that wins over some of the usual opposition, or a policy that will spread internationally through a positive feedback loop.
  • Seek support that is concentrated enough to make some nation(s) into international advocate(s) of your cause.
  • When opposing a policy, emphasize its very concrete downsides.
  • Take advantage of differences in patience—pursue policies whose lasting benefits and potentially concentrated costs will not come for years or decades.
  • When you have power, don't make the biggest positive changes you can; make changes with broad enough support to persist after you lose power.
• Given the influence of powerful actors' self-interest, people concerned with risks of extreme suffering should assign more weight to scenarios in which maintaining some form of large-scale suffering is in the interests of powerful actors, and less weight to other possibilities.
• Given the importance of de facto power for the formation/destruction of democracies, the automation of human labor at massive scales will, by default, push strongly toward the erosion of democracies.

All my takeaways should be scrutinized before use. 

Introduction and Process:

Various voiceless groups are harmfully neglected in today’s policy making. What strategies for changing this can advocates of neglected groups learn from times when excluded groups gained political protections?

People in this community have called for investigating moral and political progress. Still, before this report, there were (as far as I'm aware) no accounts familiar to this community of why countries other than the UK abolished the slave trade and slavery, of why countries around the globe became democracies, or of why these international shifts happened around the industrial revolution. This report aims to provide a summary of such an account, and to argue that it has certain implications for how we can best help neglected groups.

I examined historical case studies of global policy shifts that greatly benefited excluded groups. Of these, I focused on the abolition of the slave trade and slavery, and on extensions of the voting franchise over economic lines. Drawing on these case studies, I propose and argue for a qualitative, rational-choice model that makes predictions about political inclusion. In the full report, I discuss implications in more detail.

Context and Acknowledgements:

This comes from the research I did over the summer, through a university program.

I'm not a professional historian, so, to an even larger degree than usual, all important implications should be heavily scrutinized and considered together with other analyses.

For more caveats and acknowledgements, as well as sections on the case studies, please see the full version of this report.

Qualitative Model—Contributors to Political Inclusion/Exclusion:

The cases studied back the following model of political inclusion/exclusion. After introducing the model, I offer supporting historical examples, some elaboration on implications for moral circle expansion, and responses to two potential objections.

More details about the case studies and how the model connects to my takeaways, as well as citations, can be found in the full report.

Motivation:

A policy shift that’s particularly valuable for any group is political inclusion—a relatively durable increase in a group’s political power, e.g. legal protections or political representation. While a group is excluded, its interests aren't reliably considered in policy making, making political inclusion particularly valuable for any group.

Given the importance of political inclusion—the wide range of benefits it lastingly brings—it would be useful to know what makes shifts to political inclusion happen and last.

Background and Assumptions:

This model aims to make predictions about when transitions to political inclusion are more likely to occur and persist. It’s inspired by Acemoglu and Robinson’s (2005) model of democratization, and it focuses on particularly durable forms of political inclusion: legal protections and political representation. The model’s main assumptions are the following:

• Two groups are the primary political actors.
• One group decides whether to include or exclude the other group (which may already be included or excluded). This decision results mostly from what one group perceives as the material costs and benefits to itself of including or excluding the other group.

Generally, factors that make transitions to one state (inclusion or exclusion) more likely also make transitions away from that state less likely, so we can usefully group together factors that favor the occurrence and persistence of inclusion/exclusion.

The Model, Condensed:

The above framework suggests that the following factors, when high, make it more likely that transitions to greater political exclusion will occur and persist:

• The degree of existing/potential profitable exploitation of the group under consideration
• The costs of existing/potential inclusion (e.g. higher taxes)
• Exclusive values (e.g. during/after war)

The framework also suggests that the following factors, when high, make it more likely that transitions to greater political inclusion will occur and persist:

• The capacity of a vulnerable group to effectively resist transitions to/perpetuation of exclusion (strengthened by high coordinating capacity and vulnerable authorities)
• Potential strategic alliances between an excluded and an included group (e.g. the vulnerable group, if included, would militarily/economically benefit the included)
• Inclusive values (civil liberties are very helpful for the emergence of these)
• Inter-societal pressure for inclusion (motivated by inter-societal inclusive values, strategic alliances, or desires to otherwise reduce rivals’ profits)

We can represent this with a picture:

Some factors create incentives that weigh the balance toward exclusion being more frequent, while other factors weigh the balance toward inclusion being more frequent.

This model has important limitations.

Historical Examples:

The above model has significant support from the case studies that informed it. In the cases studied, each of the factors identified above (or their absence) seem to have  repeatedly had the predicted effect on transitions to inclusion or exclusion. The model was informed by the case studies, making this accuracy less surprising, but the framework's simplicity suggests that its accuracy is not a mere case of overfitting. 

Examples of opportunities for profitable exploitation favoring political exclusion:

• The mass enslavement of Africans for transatlantic trade was uniquely profitable (the limited availability of guns made enslavement unusually cheap, while the large labor shortage in the American tropics made returns unusually high).
• In Haiti, the US South, the French colonial empire, and the Ottoman empire, slavery was abolished only once the government—which greatly profited from slavery—was violently replaced. In contrast, slavery was abolished relatively early in regions where it was less profitable (e.g. New England, parts of Europe).
• The use of intergenerational resources and farmed animals has been highly profitable.

Examples of high costs of inclusion favoring political exclusion:

• Throughout the Western hemisphere, states with more economic inequality (where elites had more to lose from populist democracy) were slowest to democratize, and they frequently reverted to rule by the few.
• In another case where high costs of inclusion were absent—the passage of laws protecting children from cruelty (not including child labor)—political protections came very quickly after organizations began advocating for them.

Examples of exclusive values contributing to political exclusion:

• Dehumanization, especially during war, has been a frequent contributor to genocide and other forms of political exclusion.
• Racism has helped sustain race-based systems of oppression.

Examples of effective resistance contributing to political inclusion:

• In Haiti, slaves used violent revolt to abolish slavery.
• Slave resistance was a significant motivator for British abolition and emancipation. The British abolished the slave trade 2-3 years after the most successful slave rebellion in history forced Napoleon’s forces to retreat from Haiti, and British emancipation was passed 1-2 years after the British Empire faced its largest slave rebellion ever, in Jamaica.
• Slave resistance more generally increased security and supervision costs, especially for certain types of labor (e.g. for labor tasks that were profitable in New England and Canada, as well as in industrial societies). This contributed to the reduced economic viability of slave labor in these societies.
• Most cases of democratization throughout history came through the disenfranchised organizing to directly threaten the elite’s interests.
  • When and where the capacity of the disenfranchised to resist has increased, democratization has been more frequent.
• In major cases when the voting franchise was contracted (i.e. shrunk), a common feature was that the wider public had recently lost its ability to resist exclusion through ordinary lawmaking processes, because progressives who represented the wider public lost popular support.
  • This seems to have occurred in the First and Second French Republics, in the Reconstruction Era US South, in 1880s Colombia, and in 1920s Hungary.

Examples of strategic alliances contributing to inclusion:

• In Central and Eastern European states, rulers ended serfdom to avoid its perceived contributions to military weakness, presumably through serfs’ influence.
• In France, the US, and Cuba, a major motivation for emancipation was gaining the military support of slaves (or at least stopping their opposition).
• Frontier states in the US, competing for settlers who would fill their labor shortages, democratized quickly. When older colonies democratized (later), a major motivation was wanting to gain more loyal support for militias, and perhaps for political parties, from the formerly disenfranchised.

Examples of inclusive values contributing to inclusion:

• The UK, New England, and Puerto Rico had influential abolitionist associations that pushed for emancipation. In contrast, domestic pressure against slavery was largely non-existent in states that lacked strong protections for civil liberties (e.g. authoritarian France, the US South, and many societies in Africa and Asia).
• Early advocates of children’s protection seem to have had highly humanitarian concerns.

Examples of inter-societal pressure contributing to inclusion:

• Inter-societal pressure motivated by inclusive values: Europe and especially the UK internationally promoted antislavery. International sanctions on South Africa’s apartheid regime may also have been an example of this.
• Inter-societal pressure motivated by strategic alliances: states such as Spanish Florida offered freedom to slaves who ran away from rival colonies.
• Inter-societal pressure motivated by desires to reduce rivals’ profits: British plantation owners supported diplomatic efforts to ban the importation of slaves to their competitors’ plantations, and anti-colonial states later promoted antislavery in European empires.

More on Implications for Moral Circle Expansion:

Idealistic theories of moral circle expansion (e.g. Singer's) are prominent within this community. Some take them to mean that it’s highly plausible—perhaps inevitable—that inclusion will continue expanding, until the interests of currently neglected groups have entered into decision makers’ consideration. For example, applying this idea to concerns over animal welfare, 80,000 Hours writes:

Will the future be better? [...] moral concern for other beings seems to have increased over time — the ‘expanding moral circle’ — so we expect that people in the future will have more concern for animal welfare

Historical case studies of inclusion cast doubt on these arguments. As argued above, the existing or potential influence of the excluded was usually a major force driving inclusion, at least for the abolition of slavery and economic extensions of voting rights. Inclusion so frequently required powerful actors to be coerced, violently replaced, or otherwise incentivized that theories which focus on benevolence completely miss most of the historical motivators of inclusion, at least in the cases studied. 

The historical evidence here more strongly suggests a new theory of moral circle expansion: 

• Various factors—especially the resistance of the excluded, the potential for elites to ally with the excluded, and perhaps some inclusive values—motivate transitions toward greater political inclusion.
  • These transitions toward greater political inclusion tend to persist, largely because political power, once given, is uniquely difficult to take back.
• After political inclusion occurs, social values change retroactively to be more inclusive. There are several ways in which this might happen:
  • The formerly excluded group might use its new power to spread values that are inclusive to itself, to avoid being re-excluded.
  • People would internalize more inclusive norms.
  • Influential organizations might invest ideologically in the new inclusion, making it difficult (psychologically and for public relations) for them to oppose it.
  • The inclusion of a group destroys businesses that depended on exclusion, leaving fewer organizations motivated to spread exclusive values.

The first part of this hypothesis—on the causes of inclusion—is supported by the historical case studies and model reviewed earlier. The second part of this hypothesis remains speculative. Still, it involves highly plausible mechanisms, fits actual historical cases of inclusion much better than hypotheses which (wrongly) claim that inclusive values generally preceded political inclusion, and is plausible in light of findings in moral psychology.

If this view is correct, prospects for the inclusion of future generations and other totally powerless groups are not very bright. After all, both domestically and internationally, groups with no capacity to exert influence can’t effectively resist exclusion, and they are not appealing allies. In these cases, then, political actors have fewer potential motivators for inclusion, but no fewer potential motivators for exclusion. The following picture illustrate this:

Extrapolating from the past inclusion of influential groups to the future inclusion of voiceless groups would be pretending that these differences are of little importance.

Counterargument—Timing: 

One might object to the above arguments: if progress toward greater inclusion has been caused mainly by the influence of the excluded, why has most inclusive progress happened over the last few centuries? This, very plausibly, has been mostly because economic growth—especially industrialization—has greatly increased the ability of excluded humans to gain and hold on to political inclusion. 

One way that industrialization probably favors inclusion is by strengthening excluded groups. Industrialization improves communication technologies, and it drives increases in population density. These make it easier for excluded groups to organize resistance. Economic growth also seems to empower some newly wealthy actors to demand civil liberties, and these also make it easier for other excluded groups to organize resistance. 

Industrialization may have also favored inclusion by causing elites to be more vulnerable to resistance, making exclusion less appealing. Slaves can more easily mess up industrial tasks than agricultural ones. Similarly, riots of the disenfranchised do not threaten landowners’ wealth as much as they threaten the machinery and human capital that makes up the wealth of industrial elites. In brief, we can explain the timing of these modern era increases in inclusion through the impacts of industrialization: making excluded groups more able to resist exclusion, and making makes elites more vulnerable to conflict. Together, these effects make it much costlier for elites to continue violently repressing excluded groups, incentivizing elites to accept the alternative: accepting others' demands for political inclusion.

Counterargument—Apparent Counterexamples: 

One might also object: if inclusive values are not very strong contributors to inclusion, then why have there been many policy shifts that greatly benefited powerless groups, including future generations? Actually, other historical events may appear to have been successes for the inclusion of voiceless groups, but they were mainly successes for groups that were already powerful. As argued earlier, environmental conservation and the early governance of genetic engineering (as well as children’s protection, to a lesser extent) seem to have been largely done for the benefit of existing, powerful actors. 

Other policies that may seem to have helped future generations probably did not do so for their sake. Action on climate change has been highly limited, and the limited action that has been taken may have resulted from the great importance of climate change for present (empowered) generations. Other major successes of environmentalism have also offered (and emphasized) significant benefits for already powerful actors: the regulation of directly harmful pollutants, and ecological modernization. In these cases, future generations mainly got lucky, so these events are not strong evidence for a reliable trend of ever-broadening benevolence favoring the inclusion of future generations.

Appendices and Bibliography:

• This spreadsheet contains graphs, data, and elaboration (with sources) on demographic trends in slavery over the past two centuries, globally and in the US.
• Here is the bibliography of this report.