Israel says it has a right to defend itself. But does it have a right to invade Lebanon?

Since the start of Israel’s invasion of Lebanon last month, debate has swirled about the wisdom of Israel’s two-front strategy amid the ongoing conflict in the Gaza Strip, the threat that the fight against Hezbollah poses to civilians and the risk it could ignite a war with Iran.

But perhaps even more fundamental is the question of whether Israel’s invasion is legal under international law.

Israel says that it has the right to defend itself, citing a year of rocket attacks by Hezbollah from Lebanese territory. Some of its critics disagree.

A UN truck passes buildings destroyed by Israeli airstrikes on Thursday in Kafra, Lebanon.Credit: Getty Images

“Legality is very much in the eye of the beholder,” said Hugh Lovatt, an expert on international law and armed conflict at the European Council on Foreign Relations. “Does Israel’s right to self-defence trump Lebanon’s right to sovereignty? We can go around and around this circle.”

Additionally, some experts say, self-defence has its legal limits, especially if Israel’s use of force in Lebanon is disproportionate to the threat or if it fails to prioritise the protection of civilians.

“You have a right to self-defence, but you have to exercise this self-defence in a certain way,” said Judge Kai Ambos, a law professor at the University of Göttingen in Germany, who serves on a tribunal at The Hague that prosecutes war crimes committed in Kosovo during the 1990s. “It’s not limitless.”

Here is a look at some of the legal questions surrounding Israel’s invasion.

What does international law say?

Article 2(4) of the United Nations Charter “prohibits the threat or use of force and calls on all members to respect the sovereignty, territorial integrity and political independence of other states.” But Article 51 also makes clear that member states have a right to defend themselves from armed attacks.

There are more complications. Lebanon is a sovereign state, but Israel says it is fighting Hezbollah, which is both a militant group and an influential player in Lebanon’s government. (Israel, the United States and Australia consider it a terrorist organisation.)

Israel has been in violent conflict with Hezbollah since the group was founded in the 1980s, with help from Iran, to fight Israel’s occupation of Lebanon.

Most recently, after Hamas led the October 7 terrorist attacks, Hezbollah began firing rockets and missiles at Israel in solidarity with Hamas. Israel returned fire, and the two sides carried out nearly a year of exchanges. Civilians and combatants in Israel and Lebanon were killed, and more than 150,000 people displaced on both sides of the border.

Some experts say the invasion is legal because Lebanon allows Hezbollah to use its territory to strike Israel.

In light of the Hezbollah rocket and missile attacks, “Israel has the legal right to take self-defence measures against Hezbollah, and probably also against the Lebanese state,” Amichai Cohen and Yuval Shany, two Israeli law professors, wrote in an essay published for the Lieber Institute for Law and Warfare.

In an email, Shany said the United States and its allies had used similar reasoning to “operate in Syria against ISIS and in a number of other countries who had al-Qaida presence”.

“As we note in our piece,” he added, “the case for self-defence in Lebanon is even stronger.”

Humanitarian legal protections

Separate from questions about the legality of Israel’s invasion, every country has a legal obligation to safeguard civilians during warfare.

Even if Hezbollah places military targets in civilian buildings, experts say Israel must consider the safety of the noncombatants inside when it conducts airstrikes. (International law does not distinguish between ground invasions and airstrikes — the measure is “use of force,” according to Oona Hathaway, a professor of international law at Yale University.)

The United Nations says more than 1,500 people have been killed in Lebanon by the Israeli military in the past two weeks, including hundreds of deaths in a single day in September, during one of the most intense air raids in recent warfare.

Enforcing the law

It is difficult, if not impossible, to enforce international laws of war when nations disagree on how, or even whether, to act against violations.

The International Court of Justice allows lawsuits to be brought against states accused of violating treaties, such as the genocide charges South Africa has lodged over Israel’s military operations in Gaza.

Were a case to be referred to the international court over Israel’s military operations in Lebanon, Ambos said, Israel could refuse to comply with the outcome. That could send the dispute to the Security Council to be enforced.

The UN General Assembly could also be asked to seek a resolution, Hathaway said. But it does not have the authority to take action against Israel except to call on member states to do so.

“The question is, who will enforce this?” Ambos said.

This article originally appeared in The New York Times.