The question of whether, and how, democracy can survive in divided societies has long been a source of controversy in political science. Some of the greatest political thinkers have argued that stable democracy is possible only in relatively homogenous societies. Since ethnic identities tend to be invested with a great deal of symbolic and emotional meaning, aspiring politicians hungry for electoral success have strong incentives to harness these identities as a political force. Rather than converging on the mythical ‘median voter’ (Downs 1957), divided societies tend to exhibit ‘polarised pluralism’ (Sartori 1976), with competition for votes taking place at the extremes rather than at the centre.

The logic of elections in such polarised societies thus changes from one of convergence on policy positions to one of extreme divergence. With no median voters, politics can quickly come to be characterised by centrifugal forces, in which the moderate political centre is overwhelmed by extremist forces.

While this model was developed with ethnically-divided societies in mind, it also bears a strong resemblance to contemporary cases of political polarisation, not least in the United States. There, partisan allegiances have taken on an identity-like status for many Americans (Mason 2018). For instance, opinions polls routinely find Democratic and Republican voters hold sharply negative views of the other side. Questions that have long been used by researchers of race and ethnicity (such as “would you be comfortable with your son or daughter being in a mixed relationship?”), are now registering similar levels of social anxiety for party ID to those once reserved for the idea of interracial marriage (McCoy and Press 2022).

In an age of hard-line partisanship, with fewer “floating voters” between the two parties than in the past, many U.S. elections are less a battle of ideas and more a statement of identity -- like those in divided societies. Electoral campaigns promoting us-versus-them divisions have become an effective way to mobilise voters, and easier to instigate than those based on compromise, deliberation and restraint (Bartels 2020). Instead of broad-based representation, the result is increased partisan rancour, ideological rigidity and legislative polarisation (Lublin and Reilly 2023).

Is it possible to design political systems which, instead of rewarding such divisions, promote accommodation, moderation and centripetal, centre-based politics? One promising approach is to strategically design institutions such as the electoral system. My book Democracy in Divided Societies showed how changes to election rules – for example, the introduction of electoral systems which facilitate cross-partisan communication, bargaining and inter-dependence between rival politicians and the groups they represent – can promote more responsible politics, and enhance democracy, even in divided societies.

The importance of electoral system design

All societies are inherently conflictual to some degree. Democracy itself operates as a system for managing and processing conflict (Przeworski 1991). Representative institutions allow conflicts to formulate, find expression and be managed in a sustainable way via institutional outlets such as political parties and legislatures, rather than being suppressed or ignored. The design of political institutions is thus of paramount importance in any democracy.

This insight raises the prospect of engineering electoral rules to improve the fair operation of political processes and institutions. For the electoral engineer, institutions change outcomes and changing formal political institutions can result in changes in political behaviour and practice. Different electoral systems can encourage politicians and candidates to pursue starkly different avenues to electoral success: civil or hostile campaigns, broad or narrow policy agendas, cooperative or divided legislatures. This explains the scholarly consensus that “if one wants to change the nature of a particular democracy, the electoral system is likely to be the most suitable and effective instrument for doing so” (Lijphart 1995, 412).

The role of democratic institutions as the mediating agents which can process divergent interests and preferences into moderate, centripetal outcomes becomes paramount. For example, legislatures are likely to be more functional when many politicians owe their victory not just to their own diehard supporters but also those from other parties, who they may need for their re-election. Politicians who have had to bargain with their counterparts for mutual support at elections are likely to be amenable to doing the same once in government.

By strengthening the ‘moderate middle’ at the expense of the extremes, the right political reforms can help address the widespread problems of polarisation that has plagued the United States in recent years. Many political scientists see the standard U.S. electoral arrangements—closed party primaries followed by plurality general elections—as exacerbating political polarisation and extremism by enabling motivated partisan ideologues (who usually comprise only a small share of the overall electorate) to choose primary winners. As most Congressional and state legislative races are relatively uncompetitive, victory in the primary usually results in victory in the general election, giving candidates limited incentive to pitch appeals beyond their core supporters (Gehl and Porter 2020).

Plurality voting is also a classic zero-sum game: more votes for my opponent means fewer votes for me. Ranked choice voting, by contrast, offers the potential for a positive-sum game: a candidate can benefit from ballots cast initially for someone else, if those votes return to her in the form of second or later rankings. Over time, this can encourage the formation of pre-electoral coalitions, resulting in potentially enduring “coalitions of commitment” in government (Horowitz 1985, 365-95). There is evidence of both practices occurring under the century-long use of RCV in Australia, via both formal and informal pre-election coalitions underpinned by ranking exchanges (Sharman, Sayers and Miragliotta 2002).

Such mutual reciprocity should also, in theory, promote more moderate political outcomes (Horowitz 1991; Reilly 2001; Mann and Ornstein 2012; Diamond 2015; Drutman 2020; Lublin and Reilly 2023). In most cases, the way to attract wider support is to adopt more centrist or “catch all” policy positions which appeal to the median voter. The exception is where more votes are lost by such moderation than are gained, which is always a possibility in very safe districts or in places with entrenched ethnic polarisation. But in most cases, politicians seeking to gain additional votes from non-core supporters should have an incentive to moderate their political rhetoric and broaden their policy positions to pick up additional voter support. (Reilly 2001, 2018).

This kind of cross-party “vote pooling” -- the exchange of preferences between supporters of different candidates or parties -- which underpins moderation can occur under a range of electoral systems. But they are most likely to occur if some kind of ranked-choice ballot is present.

The importance of ranking

By giving voters the opportunity to express their preferences not just for but also between parties and candidates, ranked ballots have attracted significant enthusiasm from political thinkers, going back to Britain in the 19th century. Contemporary political theorists agree: McLean (1987, 154), for instance, argues that some facility for preference ordering is one of three basic requirements of a good voting system.

For most voters, the major advantage of a ranked ballot is that they do not need to be strategic about expressing their true choices. In plurality elections, by contrast, voters for smaller parties (and sometimes larger ones too) are often faced with an acute dilemma: should they vote sincerely for their true choice, even if that party or candidate is unlikely to win? Or should they instead abandon their favourite and strategically vote for the least-worst option amongst those who have a chance? While a ranked ballot doesn’t completely eliminate the potential for strategic voting, in general, voters can simply express their preferences honestly in the knowledge that voting sincerely can never hurt their chosen candidate.

Of the ten major electoral systems used in the world today, three enable electors to rank-order candidates on the ballot in this way: the alternative vote (AV), the most widely used form of RCV in the U.S. and also used for over a century in Australia, and also in Ireland for president and (in slightly different form) Papua New Guinea; the supplementary vote (SV), previously used for mayoral elections in the United Kingdom and presidential elections in Sri Lanka; and the single transferable vote (STV), as used in Ireland, Malta and most upper houses in Australia, which is a system of proportional representation. All share a common feature: they enable electors to not only choose their favoured candidate but also indicate their preference between others. It is this particular feature that distinguishes preferential voting from other electoral system options.

In examining the electoral history of all the divided societies which utilise such ranked ballots -- Papua New Guinea, Northern Ireland, and Sri Lanka as well as ‘one-off’ or short-lived cases such as Estonia, Bosnia, and Fiji – as well as other examples of established democracies in Australia, Europe and North America, it’s clear that vote pooling does indeed encourage viable steps towards inter-ethnic cooperation and conflict management in some countries. Yet not all preferential systems are equally effective at promoting accommodation in divided societies.

Case study: Papua New Guinea

One key test of ranked ballots came from a somewhat obscure case, that of Papua New Guinea. An ethnically-fragmented state in the South Pacific, Papua New Guinea’s first three elections – in 1964, 1968 and 1972 – were conducted under similar AV rules to that used in Australia, its colonial administrator until independence in 1975. These ranked ballot elections revealed a distinctive approach to campaigning in what is a traditional clan-based society. Candidates from smaller clans or those without a large ‘core’ vote often campaigned outside their home base area for other voters’ second preferences. In other cases, traditional tribal alliances enabled aligned candidates to cooperate and aggregate support without the vote being ‘split’ several ways among competing candidates.

This “vote-pooling,” i.e. exchanges of ranked preferences among candidates and their supporters, was a positive factor in a young and barely-developed democracy. But these advantages declined sharply when AV was replaced by plurality voting in 1975. With incentives for campaign cooperation removed, ethnic groups reverted to their traditional hostilities. The return to conflict was magnified by the way plurality elections work to reward vote-splitting in a fragmented society. Candidates who previously campaigned broadly and encouraged the swapping of rankings with supporters of other candidates instead focused their energies on maximising their clan-based vote. This led to a sharp increase in electoral violence, increasing number of split votes among “spoiler” candidates, and politicians being elected on alarmingly small pluralities, sometimes as little as 6 percent of the vote (Reilly 1997, 2002).

In 2003, Papua New Guinea changed back to another ranked ballot method and studies found a sharp decline in campaign violence, increased cooperation during election campaigning and the election of more broadly-supported and representative leaders.

Case study: Northern Ireland

Northern Ireland too can be judged a successful case of vote-pooling between candidates and their supporters under its proportional ranked choice system, the Single Transferable Vote. The Northern Ireland case has been extensively researched (McGarry and O'Leary 2004; O’Leary 2013, Mitchell 2014), and most find little vote-pooling prior to the ‘Good Friday’ Agreement which ushered in the power-sharing executive. Analysis of the first election suggests that preference-vote transfers served to give voice and representation to the ‘moderate middle’ sentiment for peace, and to translate this sentiment into an electoral majority for ‘pro-agreement’ parties. After that, election transfers across the sectarian divide between the main moderate unionist party and the main moderate nationalist one increased sharply, particularly from unionists to nationalists.

Other cases are less positive. Sri Lanka has used a preferential system to elect its president for over 40 years, throughout devastating civil wars and natural disasters, but the frontrunning candidate has always won an outright majority of first rankings, meaning that the system has yet to be really tested. Bosnia and Estonia both used ranked voting in one-off uses, for parliamentary elections in Estonia (1990) and sub-regional presidential polls in Bosnia (2000), before reverting to unranked systems. Fiji ran two elections under a hybrid ranked ballot system which gave parties, not voters, too much power in allocating rankings – a move which some blamed for the 2000 coup against the elected government. Following another coup in 2006, Fiji abandoned the system, and has recently return to elected government using list proportional representation.

While varying widely, one lesson from all of these cases is that stability matters for electoral rules, with voters and candidates alike needing several iterations of using ranked systems to properly utilise its potential.

Ranked ballots and their discontents

Critics of ranked ballots tend to focus on these short lived cases, sometimes arguing that vote-pooling systems are inherently unstable or unpredictable. But the century long Australian and Irish experiences, and indeed the growing body of evidence from the United States, suggests the contrary – that ranked voting can actually make politics more stable and predictable.

A more subtle critique holds that the idea of centrist politics relies on simplistic median voter models which ignore the complexity and multi-dimensionality of contemporary politics in advanced democracies such as the U.S. (Santucci 2021). But even in a multi-dimensional policy space featuring voters and activists with competing preferences or ideologies, a vote-maximising equilibrium position exists (Miller and Schofield 2008), and ranked systems are far better at identifying this than a straight plurality contest.

The virtues of political aggregation and centrism are appealing for those schooled in the Anglo-American tradition of two-party politics, where centripetal reforms can be seen as being compatible with majoritarian political models. This may help explain its current popularity in the United States, where single-member RCV has been adopted in two states – Maine and Alaska – and dozens of cities, and studies have shown a very similar impact in terms of civility and countering polarisation to that found in the literature on ethnically-divided societies (see for instance Donovan et al 2016; John et al 2018; Reilly 2021; Reilly, Lublin and Wright 2023). Ranked choice voting is more an evolutionary than a revolutionary reform, which may be why it has emerged as a viable reform option in the United States.

According to the United Nations, over three-fifths of the world’s population will be urban by 2030. This worldwide trend of rural => urban migration towards multi-ethnic ‘world cities’ appears to be leading inexorably towards the development of massive, ethnically-heterogeneous urban metropolises as models of human settlement in the 21st century. As ethnic groups increasingly find themselves in close physical proximity but separated by growing distinctions, so ranked ballot elections facilitating inter-ethnic accommodation is likely to become an increasingly attractive option for constitutional engineers worldwide.