Just short of his 80th birthday, Rodrigo Duterte, a man who once vowed to purge his country through a bloody anti-drugs and crime campaign, found himself outmanoeuvred and in custody.

The former president was met by Philippines police as he arrived in Manila on a flight from Hong Kong, where he had been rallying support for his candidates for the upcoming mid-term election among the large Filipino diaspora there.

The much-talked-about warrant for his arrest from the International Criminal Court (ICC) was, it turned out, already in the hands of the Philippines government, which moved swiftly to execute it.

A frail-looking Mr Duterte, walking with a stick, was moved to an air force base within the airport perimeter. A chartered jet was quickly prepared to take him to the ICC in The Hague.

How had this happened? How had a man so powerful and popular, often called “the Trump of Asia”, been brought so low?

In vain, his lawyers and family members protested that the arrest had no legal basis and complained that Duterte’s frail health was being neglected.

While in office, Mr Duterte formed an alliance with the Marcos family – the children of ousted dictator Ferdinand Marcos who had long been working on a political comeback. Mr Duterte could not run again in the 2022 election, but his daughter Sara, mayor of southern city of Davao, was also popular and a strong contender to replace him.

However, Ferdinand Marcos’s son Bongbong, who had been in politics all his life, was also well placed to win and very well-funded.

The two families struck a deal. They would work together to get Bongbong into the presidency and Sara into the vice-presidency, on the assumption that come the next election in 2028, her turn would come and she would have the formidable Marcos machine behind her.

It worked. Both won their positions by a wide margin. Mr Duterte expected that his alliance would protect him from any blowback over his controversial presidency once he was out of power.

The most serious threat hanging over him was an investigation by the ICC into his culpability for thousands of extrajudicial killings carried out during anti-drugs campaigns he ordered – after he became president in 2016, but also during his tenure as mayor of the southern city of Davao from 2011.

Mr Duterte withdrew the Philippines from the jurisdiction of the ICC in 2019, but its prosecutors argued they still had a mandate to look into alleged crimes against humanity committed before that, and launched a formal investigation in 2021. However, President Marcos initially stated that his government would not co-operate with the ICC.

That position only changed after the dramatic breakdown of the Duterte-Marcos alliance. Strains in their relationship were evident from the earliest days of the administration, when Sara Duterte’s request to be given control of the powerful defence ministry was turned down and she was given the education ministry instead.

President Marcos also distanced himself from his predecessor’s mercurial policies, mending fences with the US, standing up to China in contested seas, and stopping the blood-curdling threats of retribution against drug dealers.

In the end, these were two ambitious, power-hungry clans aiming to dominate Filipino politics, and there was not enough power for them to share. Relations reached a nadir last year when Sara Duterte announced that she had hired an assassin to kill President Marcos, should anything happen to her.

Late last year, the lower house of Congress, which is controlled by Marcos loyalists, filed a petition to impeach Ms Duterte. That trial is due to take place in the Senate later this year.

If she is impeached, under the constitution, she would be barred from holding high political office, killing her long-standing presidential ambitions and weakening the political power of the Dutertes even further.

President Marcos now appears to have moved deftly to neutralise his main political rival. But his strategy is not risk-free. The Dutertes remain popular in much of the country, and may be able to mobilise protests against the former president’s prosecution.

Sara Duterte has issued a statement accusing the government of surrendering her father to “foreign powers” and of violating Filipino sovereignty.

An early test of the support enjoyed by both clans will be the mid-term elections in May.

In his comments to journalists after the plane carrying his predecessor had taken off from Manila, President Marcos insisted he was meeting the country’s commitments to Interpol, which had delivered the ICC. But he was coy about the fact that it was an ICC warrant he was executing, given that many Filipinos will question what the ICC’s remit is in a country which has already left its jurisdiction.

It is not risk-free for the ICC either. The court is an embattled institution these days, with the Trump administration threatening to arrest its top officials should they travel to the US, and few countries willing to extradite those it has indicted. Getting former President Duterte to The Hague might therefore look like a welcome high-profile success.

But there was a warning, from China – admittedly not a signatory to the ICC and currently at loggerheads with the Philippines – not to politicise ICC cases. This was a thinly-veiled reference to the fact that this case, which is supposed to be about accountability for serious international crimes, has ended up playing a decisive part in a domestic feud in the Philippines between two rival political forces.