Spain is heading into an election on 28 April with the divisions created by Catalonia's 2017 breakaway bid still raw -- and it is not just the rift between separatists and the state that is shaping this campaign.

Catalan society itself is split down the middle, much like Brexit in the UK, and, in the rest of the country, tension is boiling between those backing reconciliation and hardliners demanding central government wield its power.

Investors will be rooting for a clear outcome and a stable government after more than three years with a paralysed executive. Yet the Catalan crisis has triggered an outburst of nationalism that has spawned a new party, Vox.

For the first time, Spain has five significant parties to watch -- two of them with a populist origin story.

Complicating the process of coalition building is the fact that parties are split along ideological lines, as well as on Catalonia. That has made the position of Catalonia's non-separatist Ciudadanos party, a potential kingmaker straddling both worlds, much more difficult.

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Here's an overview of the key players.

The Socialists

Prime minister Pedro Sanchez's efforts to repair divisions over Catalonia's push for independence has taken up most of his nine-month tenure. His harshest opponents label him a traitor because he needed the separatists' votes to win last year's no-confidence vote.

While in office Mr Sanchez issued a raft of decrees on socially progressive issues, snatching potential voters from his left-leaning parliamentary ally, the anti-austerity Podemos. They include increasing paternity leave, tracking gender pay gaps and populating his Cabinet with a record number of women.

Podemos

Podemos burst onto the Spanish political scene in 2014 in the wake of the financial crisis. Its promises to delay the pace of deficit reduction, subsidise public transport for the poor and increase taxes for the rich were a hit with voters worn down by high unemployment and cost-cutting. The party's latest proposals include capping the working week at 35 hours and providing economic assistance for victims of gender violence.

The party backed Catalonia's right to hold a referendum on independence, although it said the vote would not be binding. Leader Pablo Iglesias angered the right-of-centre parties by meeting with jailed separatist leaders last year.

Ciudadanos

The party born in Catalonia has made confronting separatists its raison d'être. It surged in popularity by demanding harsher measures to contain the revolt while then-prime minister Mariano Rajoy dithered.

On social issues, its policies do not differ much from the Socialists. The party proposes free school books, increased financing for universities and student grants and to gradually increase the duration of paternity leave as well as fighting against gender violence.

People's Party

Mr Rajoy was slammed from all sides as he tried to contain the Catalan uprising following an illegal referendum, eventually invoking emergency powers to rule the region from Madrid. Pablo Casado, now at the helm of the party, vows to suspend Catalonia's autonomy.

The PP has long been the bastion of conservative, Catholic values in Spain. Threatened by the rise of Vox, Mr Casado has been trying to compete with the insurgent by adopting a stance against abortion and immigration while trying to keep business on side with tax-cut promises.

Vox

The new kid on the block, Vox surged in popularity in Andalusia's regional elections in December by taking the hardest line on Catalan independence.

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On social issues, Vox wants to rescind a 2004 gender violence law, arguing that it discriminates against men. It seeks to ban the use of the public health system for abortion and sex-change surgery and would deport undocumented immigrants, as well as those with papers who commit serious crimes.