AS AMPHIBIOUS assaults go, the invasion of the Malaysian state of Sabah by the self-styled Royal Army of the Sultanate of Sulu on February 11th is admittedly tame. Scores of men, many heavily armed, came ashore from motorboats that had brought them from the Philippines, an hour away, where they and the sultan of Sulu are citizens. Without firing a shot, they occupied a sleepy village. There they announced that they had come to enforce the sultan’s claim to Sabah.

At first the Malaysian security forces suspected the intruders were Islamist militants (the Philippines has plenty such people in its southernmost islands). They swiftly surrounded the village. Negotiations ensued. Malaysian officials informed the Filipinos that they had entered Sabah illegally and would be deported. The men refused to go, and as The Economist went to press were still there. The Philippine government was taken aback. It denied any hand in the incursion and asked for the safe return of its citizens. To understand what it is all about, go back to 1658. Then the sultan of Brunei gave Sabah, in what is now the Malaysian portion of the France-sized island of Borneo, to the sultan of Sulu, who ruled a part of what is now the Philippines. In 1878 the sultan of Sulu leased Sabah in perpetuity to the British North Borneo Company. In 1946 the company ceded control of Sabah to Britain. Eleven years later, the sultan declared the lease void. But Sabah opted to become part of Malaysia when it gained independence in 1963. The sultan subsequently assigned his Sabah claim to the Philippines. Malaysia still pays him a token rent. Some Filipino Muslims regard with nostalgia the heyday of the sultanate of Sulu—a time before colonial rule first by Spain, then by America, and latterly by the Christian majority in an independent Philippines. The sultan, Jamalul Kiram III (there is also another claimant), is now a merely symbolic figure. His claim to Sabah is a romantic fantasy, yet one that grips the imagination of those hoping for another golden era. It was the Philippine government’s betrayal in 1968 of a plot to pursue the claim to Sabah by force of arms that provoked the rebellion by Muslims seeking independence for their heartland in Mindanao in the south of the country. The rebellion persisted for more than four decades, costing tens of thousands of lives. But last October the government and the main rebel group, the Moro Islamic Liberation Front (MILF), signed a preliminary agreement to give Muslim areas greater autonomy in exchange for peace. The agreement was brokered by Malaysia.

The Philippine government suspects that the incursion into Sabah is a plot to wreck the peace agreement. A representative of the sultan denies this was the purpose. But the sultan himself says he is upset at being excluded from the process. Suspicion also falls on another Muslim rebel group, the Moro National Liberation Front (MNLF). It made peace in 1998, but many of its fighters were never disarmed. A spokesman, while expressing support for the sultan’s claim, denies that the MNLF had a hand in the Sabah affair. However, its chairman, Nur Misuari, has frequently complained that the peace agreement between the government and the MILF has pushed his organisation to the margins.

The incursion clearly embarrassed the Philippine government in Manila. It has never renounced the claim to Sabah bequeathed to it by the sultanate. But it has let the claim lie dormant while Malaysia intercedes to bring about peace with the MILF. The Philippine and Malaysian governments are unlikely to be deterred by what seems to be an armed publicity stunt. They have a common interest in ending the Muslim separatist rebellion in the Philippines in case it once again descends into militancy. The Philippines remains awash with Muslim armed groups: the MILF, the MNLF, Abu Sayyaf, myriad criminal gangs—and now the Royal Army of the Sultanate of Sulu. Militants will be difficult to root out from an environment so disorderly that some have the nerve to try invading another country.