"In this venue, your honours, I announce my separation from the United States," thundered Philippine President Rodrigo Duterte during his historic visit to China in 2016. At the time, few, including members of his inner circle, took the remarks seriously, never mind literally.

In mid-February, however, Duterte effectively ended the country's century-old alliance with the US by unilaterally abrogating the 1998 Visiting Forces Agreement (VFA), a linchpin of security cooperation in recent decades. As one top Filipino official put it, without the VFA the Philippines's alliance with the world's superpower is "practically useless".

Duterte's latest move, which was prompted by growing diplomatic friction with Western nations over human rights issues, recklessly exposes the Philippines to a whole host of traditional and non-traditional security threats.

Without robust assistance from the US, the Philippines's decrepit, underfunded, and ill-prepared military would hopelessly struggle against the ravages of climate change, China's creeping presence in Philippine waters, and armed groups' expanding presence on the southern island of Mindanao. Instead of pushing for a more equitable and mutually beneficial relationship with a long-term ally, the Filipino president has placed personal grievances against the US above his country's national interest and long-term strategic needs.

A decades-old alliance

Although the Philippines gained independence from the US in 1946, it continued to host a large number of US troops. It became a forward deployment base for projection of US power in Asia, making it completely dependent on the US for its defence.

US military presence in the country also ensured direct US interference in Manilla's domestic affairs. Washington readily propped up the dictatorship of Ferdinand Marcos for 30 years, supporting his efforts to eradicate a Maoist uprising.

His regime collapsed in 1986, and with the subsequent end of the Cold War shortly after, there was a growing clamour for the removal of American bases in the Philippines. Nationalist elements, which dominated the Philippine Senate, along with progressive civil society groups, portrayed the US military presence as anachronistic and a strategic liability, which exposed the country to potential hostile action by enemies of the US and prevented it from becoming fully independent.

Though the bases brought significant economic benefits, including annual military aid, Washington's collaboration with the Marcos dictatorship as well as crimes by American servicemen on Philippine soil only added to the new nationalist fervour.

Following the collapse of the Soviet Union, both sides agreed to remove large-scale US bases in the Philippines.

Soon, however, it became increasingly clear that the Philippines, long accustomed to relying on the US defence umbrella, was unprepared to stand on its own.

In 1995, China took over Philippine-claimed Mischief Reef in the strategic Spratly islands archipelago in the South China Sea, which is a disputed territory between several countries in the region. Since then, the Chinese authorities have not only built infrastructure on the reef but also forcibly claimed another island in the area.

Fearing the growing Chinese military presence in the region, in 1998 the Philippine government decided to bring US troops back to its territory through the negotiation of a VFA, which provides the legal framework for the large-scale entry and rotational stationing of US soldiers.

Since then, the US and the Philippines have conducted regular joint war games and naval drills and deepened cooperation on coastguard training. The US has also expanded defence aid to as well as reiterated its commitment to assist the Philippines in the event of a conflict in the South China Sea, including attacks by Chinese militia forces against Philippine troops and vessels in the area.

The US troops in the Philippines have also helped during emergency situations. During the 2013 Haiyan Super Typhoon, which ravaged large parts of central Philippines, the US deployed 12 ships, 66 aircraft, and as many as 13,400 troops to assist communities, which could not be reached by the Philippine military and government agencies.

The US also helped out during the months-long and bloody siege on the city of Marawi, Mindanao island by fighters affiliated to the ISIL (ISIS) group. The VFA facilitated the quick and decisive deployment of US Special Forces, which trained their ill-prepared Filipino counterparts to conduct large-scale urban warfare and counterterrorism operations against a determined and well-trained adversary. The US also provided real-time intelligence, surveillance drones, and high-grade weapons, which proved crucial to the liberation of the Muslim-majority city that year.

A reckless move

The VFA has been controversial, particularly over the issue of legal immunity from prosecution granted to American servicemen by local courts. The 2014 murder of Jennifer Laude, a 26-year-old Filipina transwoman, by US Marine Joseph Scott Pemberton, particularly galvanised the Philippines public. The VFA prevented domestic judicial institutions from directly punishing the American serviceman, who has remained in US custody.

Nonetheless, surveys suggest that the US is by far the Filipinos' most favoured international partner. Even key Duterte allies in the Senate have opposed Duterte's unilateral abrogation of the agreement, instead pushing for a formal review process. Members of the Senate have questioned the legality of Duterte's decision, maintaining that since the VFA was ratified by the legislature it cannot be abrogated without their concurrence.

The way forward, many argue, is to formally review the agreement and, if necessary, renegotiate elements, which are deemed unfavourable to the Philippines.

Ignoring clear and present threats to the Philippines, which is yet to develop strategic self-defence capabilities, Duterte has suggested deepening security cooperation with the likes of China, which would richly benefit from any disruption to the Philippine-US alliance. This reckless decision puts the internal and external security of the country in danger.

Without the US assistance, China could easily move ahead with reclaiming and militarising the Philippine-claimed Scarborough Shoal, which lies just more than 100 nautical miles (185km) from key Philippine bases in Subic Bay and Clark. China's militarisation of the contested shoal, which was coercively seized from the Philippines amid a months-long naval standoff in 2012, would not only mean the definitive loss of a Philippine-claimed territory, but also the presence of hostile military assets close to the country's capital and key military and civilian facilities.

China will also continue to harass Philippine fishermen and military personnel across the South China Sea. An armada of Chinese militia vessels has menacingly surrounded and harassed Philippine personnel in the area throughout the past year. In June, a suspected Chinese militia vessel rammed a Philippine fishing boat, almost killing all its 22 occupants.

A study by the University of the Philippines's Marine Science Institute (UP MSI) shows that the country is losing more than $600m annually due to Chinese reclamation activities and illegal fishing.

Apart from China, transnational terrorist groups could also pose a major threat to the security of the Philippines in the absence of US military support. They could exploit the fragile political transition in Mindanao by stepping up their attacks.

Above all, the country faces a wide array of extreme weather conditions amid intensifying climate change potentially without large-scale US assistance.

Though Duterte and his allies have touted the VFA abrogation as a move towards an "independent" foreign policy, the reality is that the Philippines is now dangerously vulnerable to growing threats from China in the South China Sea, ISIL elements in Mindanao, and climate change across the country.

The views expressed in this article are the author's own and do not necessarily reflect Al Jazeera's editorial stance.