MADRID (AP) — Spain's acting Prime Minister Pedro Sánchez ’s chances of forming a new coalition minority government following an inconclusive election in July were greatly boosted this week after reaching an agreement with a tiny party he surely hoped he would never have to rely on.

The deal is with Together for Catalunya, also known as Junts — a group bent on achieving independence for the northeastern region of Catalonia that's headed by Carles Puigdemont, who fled Spain after leading a failed illegal secession bid in 2017 that brought the country to the brink.

Key to the agreement signed Thursday is a massively controversial amnesty that could benefit Puigdemont and thousands of other secessionists. But the proposal, backed by several smaller left-wing parties, has roused the ire of the conservative and far-right opposition parties that represent roughly half the country’s population. Many in the judiciary and police are also opposed.

Here is what you need to know about the amnesty and how it all came about.

Few details have been released of the amnesty proposal being debated between Sánchez’s Socialist party and Junts, which will have to be approved by Spain's Parliament. However, the idea is it would wipe away the legal cases against Puigdemont and thousands of others who took part in the secession bid or participated in protests, some of which turned violent, when Spain implemented a crackdown in response.

Sánchez, whose government has already granted pardons to several jailed leaders of the Catalan independence movement, says the amnesty will be positive for Spain because it will calm waters inside Catalonia. Puigdemont is one of several Catalan leaders who fled justice after an illegal independence referendum was held in 2017. An amnesty would allow the five that are still abroad, including Puigdemont, to return to Spain and even run for office again someday.

The idea of independence from Spain stretches back decades, if not centuries, for a region that is fiercely proud of its institutions, traditions, and Catalan language, which is spoken along with Spanish. It gathered momentum during the financial crisis of 2008-2013 and then peaked in 2017 when Puigdemont, as regional president, held the illegal ballot on secession and made an ineffectual declaration of independence that received zero international recognition. The nearly 8 million inhabitants of Catalonia, whose capital is Barcelona, are roughly divided over independence, although latest opinion polls in the region indicate fewer favor secession.

Given that Puigdemont is considered public enemy No. 1 for many Spaniards, and Catalan independence a politically toxic issue, some wonder why Sánchez, who has long opposed any amnesty, is now pushing for it. The answer, critics say, is pure political necessity and the desire to stay in office.

A national election in July left no party close to an absolute majority. Sánchez's Socialists with 121 seats, and their leftist coalition partner Sumar — translated as Joining Forces — with 31, need the support of several smaller parties to clinch a 176 majority in Parliament and stay in power. Those include the two pro-secession Catalan parties who led the unsuccessful 2017 breakaway attempt. Junts, with seven seats, became the key.

The chance given to Puigdemont to play kingmaker by the summer's election outcome breathed new life into his political career and his cause just when his party was losing ground inside Catalonia, where Sánchez's Socialists are on the rise.

Tens of thousands of people have staged massive protests against the amnesty in recent weeks. The demonstrations were called by the Popular Party and Vox, who accuse Sánchez of betraying the country and handing power to a fugitive. Violence broke out at rallies backed by Vox outside the Socialist Party’s headquarters in Madrid several nights in November. Police say the violence has been caused by a minority of extreme right-wing radicals. Another major protest has been called for Sunday by the Popular Party.

Under the deal signed Thursday between the Socialists and Junts, both parties recognize their vastly different points of view on the Catalan conflict but agree to work together to resolve it. Junts says it will propose holding another self-determination referendum but agrees to not do it unilaterally, like in 2017. Instead, it will be under Article 92 of the Constitution, which demands the authorization of the prime minister, the Parliament and the king. Junts also demands that more tax revenues stay in Catalonia, one of Spain's richest regions, similar to agreements signed with rich Basque Country and Navarra regions.

The two parties also agree that the amnesty must cover all those who have been subjected to judicial processes — both before and after the 2017 referendum. One clause that is seen as a possible interference in the judiciary is the mention that commissions may investigate if there were cases of "lawfare," meaning that the justice system was used for political purposes against secessionists that might require legislative modifications.

Any amnesty approved by Spain's Parliament is likely to be contested by the opposition parties and several courts in Spain. This may not immediately affect the beneficiaries of the amnesty, but it would cause a legal quagmire of gigantic proportions in an already clogged judiciary.

Meanwhile, Spain’s Supreme Court is still trying to have Puigdemont extradited from Belgium for embezzlement. On top of that, the lower National Court recently named him and another secessionist leader in an investigation into possible terrorism during the independence push.

The amnesty talks have also drawn the attention of the European Union Commissioner of Justice, Didier Reynders, who sent Spain’s government a request for more information.

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Wilson reported from Barcelona, Spain.