International law expert Michel Erpelding argues that today's breaches in Ukraine and Gaza reflect a deeper crisis of international law, rooted in post-Cold War unilateralism and the erosion of once-taboo limits such as annexation.

The basics of international law

International law originally set out to regulate relations between sovereign states. Michel Erpelding, a researcher at the Max Planck Institute for the History of International Law, explained that such rules existed long before the UN era: medieval treaties already restricted the conduct of war and protected ambassadors, and even the ancient Greek city-states applied certain norms.

Over time, however, the scope of international law has expanded. Erpelding explained that it no longer concerns only states, but also international organisations such as the UN or the EU, individuals who are protected through human rights and humanitarian law, and even companies which are shielded from arbitrary expropriation.

WWII: Paradigm shift

After 1945, international law reflected both the balance of power and efforts to restrain it. Erpelding stressed that even superpowers like the US and the Soviet Union accepted limits, recognising they could not simply invade and annex territory, as had been common between the world wars.

Other principles consolidated too: the protection of civilians in conflict, and the recognition of the dignity and rights of all peoples, whether from the West or from newly decolonised states, Erpelding stated. He noted that while this took decades to implement, especially through decolonisation, it became broadly accepted, with Palestine remaining a glaring exception.

Fall of the USSR

Erpelding made clear that although the principle was that rules should apply to all, great powers always tried to interpret them to their advantage. What changed, he said, was the end of the Cold War. With the Soviet Union gone, the United States became the dominant power and began to act unilaterally.

The clearest case was the 2003 invasion of Iraq. Unlike the 1991 Gulf War, which had a UN Security Council mandate, the Iraq war was launched without one, he said. That moment, he argued, marked a turning point where the rules were openly undermined.

Erpelding explained that the erosion deepened under Donald Trump. For the first time since 1945, the US formally recognised annexations in Israel's case, he said. According to Erpelding, annexations had been treated as absolutely illegal for decades, and this recognition shattered a taboo.

International lawyers had already warned it would "open Pandora’s box", encouraging others to follow suit, he noted. Russia's war against Ukraine is, in Erpelding's view, a textbook annexation war, something unthinkable since the Second World War.

International law in crisis

Erpelding believes international law is now in crisis on multiple fronts. The ban on aggression and annexation wars has been openly violated, he said. State equality and peoples' right to self-determination are being questioned, with Erpelding pointing to Gaza, where Palestinians are effectively denied statehood despite their legal entitlement.

He said that humanitarian law is eroding, while acknowledging that violations against civilians have always occurred. However, Erpelding makes the important distinction that there used to be attempts at accountability.

Today, even democratic states say they will not enforce International Criminal Court (ICC) warrants against figures such as Israeli Prime Minister Netanyahu, Erpelding noted. Luxembourg, he added, has taken a different stance but should assert it more publicly.

He explained that if rules are only symbolic and not enforced, they lose their value. For Erpelding, this is not unique to international law, as it mirrors the broader weakening of the rule of law, particularly visible in the US, where governments bypass both international and domestic constitutional limits.

Looking ahead, Erpelding warned that if several powerful actors all choose to flout the rules, the world could drift back to a 19th-century model where great powers dominate smaller ones, territorial wars return, and civilian life is devalued. History, he insisted, does not guarantee linear progress, as societies can always fall back into barbarism.

Restoring credibility

Yet he also sees an opportunity. The ICC and international criminal law have long been criticised for disproportionately targeting African leaders, Erpelding said, adding that several African states even withdrew from the Rome Statute in protest.

If the same rules were now applied to Western allies, including Israel, it could restore credibility, bring more countries back into the system, and reinforce accountability at national levels, he explained.

The challenge, Erpelding said, is to convince people that international law still matters. If its relevance can be demonstrated, states and citizens alike may again be willing to stand behind it, he concluded.