In March, US President Joe Biden warned Israeli Prime Minister Benjamin Netanyahu not to launch a ground offensive in the southern Gazan city of Rafah. "You can't have another 30,000 Palestinians dead as a consequence of going after [Hamas]," he told US broadcaster MSNBC, calling it a "red line."

In February 2023, EU foreign affairs chief Josep Borrell sent China a message: If Beijing delivered Moscow weapons for its war of aggression on Ukraine, a line would be crossed.

Russian President Vladimir Putin issued a similar ultimatum to Kyiv on potential NATO membership not long before the invasion of Ukraine in early 2022. And for Chinese President Xi Jinping, a major no-go for Taiwan is a formal declaration of independence.

Netanyahu himself once literally drew his red line in the nuclear dispute with Iran with a felt-tip pen. In September 2012, the Israeli prime minister warned the UN General Assembly that Tehran was on the verge of finishing a nuclear bomb. To drive his point home, he drew a red line on a picture of a bomb, representing a threshold that should never be crossed.

World's hegemonic powers sending a message

These days, it seems more and more "red lines" in international politics are being breached.

According to Smart Politics, a US data journalism website, only two US presidents before Barack Obama had ever spoken about the concept for the first time. Obama himself used the stylistic device a further 11 times. His warning to Syrian ruler Bashar Assad about the use of poison gas in the Syrian civil war is a particularly well-known instance.

For Anne Holper, a conflict researcher at the European University Viadrina Frankfurt, the increasing use of the term reflects the shifting balances of geopolitical power. Together with her Swiss colleague Dana Landau from the University of Basel, she has initiated a research project on the topic.

Holper, a conflict researcher, said it's about the hegemonic powers sending a message. "This is where you hit the point of no return if our current system of order is to hold," she said.

The use of poison gas in Syria, a possible nuclear bomb in Tehran's hands and the Russian invasion of Ukraine: all were violations that shook this world order to its very foundations, she said.

"Whenever an order that is believed to be stable is challenged, that's when red lines are most likely to be drawn. That is when the outrage is greatest," said Holper. "When you feel most challenged and compelled to make a statement with a maximum threat capacity, so the other party doesn't dare take one step further."

'The goal is deterrence'

Along with declarations of red lines often comes a threat of serious consequences — though these are often left vague. "The goal is deterrence," said Holper. In essence, it's a political bluff, but with it comes a dilemma. "You don't actually want to impose heavy sanctions, but they have to follow if the line is crossed," she said.

President Biden also left open what would happen if Israel did proceed with its Rafah ground offensive: the only threat was a reduction in military aid. Not long after, Washington rowed back the consequences, presumably to avoid not having to take action. The United States did not believe Israel's actions in Rafah represented a "major ground operation," and therefore, no red line had been crossed, the White House said.

For Holper, red lines are a paradoxical instrument. If you don't follow through on the threat "then you yourself experience a loss of credibility and power that may be much more serious than that caused by the actual transgression," she said.

Fight against shifting boundaries

So why do leaders keep drawing red lines? The global distribution of power is currently undergoing fundamental change, Holper pointed out, with the rise of Russia, China and some states in the Global South calling into question the current world order.

In particular, powers that are keen to preserve the existing world order want to prevent the "perforation of borders [...] because they know that if one person does it, others will follow." At some point that means there will be a new world order, with new rules.

But as the balance of power shifts, boundaries can no longer be maintained at all times and all places, said Holper, adding that they also reveal to what extent taboo violations can be tolerated.

From the perspective of conflict research, it's therefore not wise to make red lines public in order to use them as a deterrent. Holper said that when it comes to speaking to the outside world, communication should be kept as flat as possible to avoid escalation.

It's hard to climb down from a strong threat, she said, adding that both sides can easily be drawn into unwanted escalation.

"That's why it's better not to go there," she said.

This article was originally written in German.