Today we mark the 15th anniversary of the bloody end of Sri Lanka’s three-decades-long civil war. This anniversary comes around at a critical historical juncture, amid the humanitarian catastrophe unleashed by Israel’s assault on Gaza.

The global response to Gaza, across many states, peoples and international institutions, shows that there is a strong will to uphold international norms on protecting civilians and a strong will to address the underlying political injustices of the conflict itself, rather than seeing it merely as a problem of security and terrorism. The international failure to translate this will into concrete action is appalling but sadly not unprecedented.

The state of Sri Lanka, 15 years after the end of the armed conflict there, shows what happens when mass atrocities are unaddressed and the political fault lines that led to them in the first place remain unresolved and are arguably exacerbated. There are also striking and unavoidable similarities between the events still unfolding in Gaza and those that took place in the Vanni, the area of northern Sri Lanka where the war ended.

In the final months of the conflict, the Sri Lankan military besieged and bombarded a civilian population of 330,000 along with an estimated 5,000 Tamil Tiger fighters, corralling them into ever thinner strips of land in the Vanni. The offensive was brutal and unconstrained. It destroyed and defeated the Tamil Tigers’ armed group LTTE but also made a raging bonfire out of international humanitarian law, the laws of war and basic norms of civilian protection.

The Sri Lankan military bombed and shelled food distribution centres, hospitals and civilian shelters even though it had received the precise coordinates of these from the United Nations and International Committee of the Red Cross. It ordered civilians into ever-shrinking “no-fire” zones that it would then relentlessly attack using unguided artillery shells and multi-barrelled rocket launchers, firing hundreds and sometimes thousands of shells a day.

The last of the no-fire zones was a mere 2-3 square kilometres and the death toll often reached 1,000 civilians a day, sometimes more. Sri Lanka also limited the supply of food and essential medicines including anaesthetics in moves calculated to compound and exacerbate the humanitarian distress.

Subsequent UN investigations concluded that the Sri Lankan military’s campaign amounted to the “persecution of the Vanni population”. At least 40,000 people were reported killed in the fighting, but some estimates based on population figures suggest the death toll could be as high as 169,000.

At the end of the war, the Sri Lankan authorities summarily executed LTTE cadres and others who surrendered and herded the remaining civilians into barbed wire-ringed internment camps, allegedly for “processing”. The government only released them after immense international pressure.

Sri Lanka justified its campaign as the only way to defeat “terrorism” and proclaimed its “victory” over the LTTE as a military model that other countries could follow. It has consistently and vehemently rejected international demands for meaningful accountability and has also refused to implement political changes that would ensure real political equality for the Tamils and address the root causes of the conflict.

Yet, Sri Lanka’s trajectory after 2009 shows that mass atrocities and the “victory” they secure entail consequences that rebound and not just for the Tamil population. After the war ended, Sri Lanka simply doubled down on its repression of Tamils.

The high-intensity bombardment turned into a suffocating and all-pervasive de facto military occupation that continues to this day. Five out of seven of the army’s regional commands are stationed in the northern and eastern provinces and in some districts, there is one soldier for every two civilians.

The military is also participating in the ongoing process of “Sinhalisation” and “Buddhisisation” of the northeast. Military personnel accompany Buddhist monks and Sinhala settlers as they violently seize Tamil lands and places of worship so that they can be converted into Sinhala ones.

Finally, military personnel exercise a constant surveillance of everyday Tamil social, cultural and political activities that has a chilling effect on everyday life and makes meaningless any talk of “reconciliation” or even a return to “normalcy”.

Yet Tamils in the former war zones and the now extensive diaspora have not been cowed into submission. They have worked to keep alive the struggle for justice and accountability. These efforts have kept Sri Lanka on the back foot internationally with repeated UN investigations and resolutions at the UN Human Rights Council. Sri Lankan officials also have to live with the ever-present danger of sanctions and possible prosecutions for their involvement in war crimes and crimes against humanity.

The war and its aftermath empowered the Rajapaksa family and their unvarnished form of Sinhala Buddhist nationalism. From 2005 until 2022, they dominated the Sinhala electorate, lauded as the leaders who had finally vanquished the Tamil separatists. Yet, their reckless and nepotistic approach to the economy and international politics brought financial ruin and increasing isolation.

Colombo sought to play off the geopolitical rivalries of India, China and Western states but this failed to secure any tangible material benefits and also could not avert the escalating debt crisis. In April 2022, Sri Lanka defaulted on its debt amid acute shortages of food, fuel and essential medicines. The outrage and roiling protests triggered by the economic meltdown ousted the last Rajapaksa president but Sri Lanka is yet to find a viable or stable post-Rajapaksa settlement.

Meanwhile, the same militarisation and repression used against Tamils are now being deployed against other communities. Sri Lanka has used “high security zones” extensively in the Tamil-speaking areas to confiscate land, displace civilians and militarise public space. This same tactic has now been deployed to restrict protests in the capital city of Colombo. The anti-terrorism measures that were normally reserved for use against Tamils are now being deployed against other dissidents and critics.

In the years after the end of the war, Muslim and Christian communities have also become targets of violence and hatred. Buddhist monks have led attacks on Muslim homes and businesses and on churches. They have led campaigns against Halal meat and the headscarf. During the pandemic, Muslims who had died as a consequence of COVID-19 infection were forcibly cremated for spurious “public health” reasons.

The impunity with which Sri Lanka’s security forces operate is now a threat to all communities on the island. There is no better illustration of this than Cardinal Malcolm Ranjith’s ongoing campaign calling for an international investigation into the Easter Sunday terrorist attacks that killed 250 people.

Cardinal Ranjith had previously been a staunch Rajapaksa ally and had opposed Tamil demands for international accountability for the crimes committed at the end of the war. He is now calling for an international investigation because he is convinced, like many on the island, that elements of Sri Lanka’s security state were aware of the plans for the appalling Easter Sunday attacks but did not take action in order to bolster the eventually successful 2020 presidential campaign of Gotabaya Rajapaksa.

The effects of Sri Lanka’s massacres have extended well beyond May 2009 and the killing fields of the Vanni. They are evident in the ongoing de facto occupation of the Tamil-speaking areas by a military that eats up the scarce resources of a now effectively bankrupt state. They are evident in the political instability and growing repression in Colombo. They are also evident in security forces who have become such a power unto themselves that they have been accused by a formerly loyal cardinal of allowing brutal terrorist attacks to take place to secure electoral victory for their preferred candidate.

Israel’s assault on Gaza has rightly brought international attention and focus on the need to uphold and defend humanitarian law. Sri Lanka shows what happens when states that commit mass atrocities are allowed to go scot-free.

Remembering and effectively addressing the Vanni atrocities is not just about the past, it is also about the future. Most immediately, it is about Sri Lanka’s future. But it is also about re-building and securing the viability and integrity of international humanitarian law and the possibility of securing genuine and lasting peace, security and prosperity.

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