A leading international law expert believes New Zealand has been slow to sign up to an agreement making a state which carried out a crime of aggression subject to the International Criminal Court.
Roger Clark said had the agreement been in place years ago it is likely Britain would have been more reluctant to go to war in Iraq.
In 2002 the Rome Statute established the International Criminal Court (ICC), a permanent tribunal to prosecute individuals accused of the most serious crimes such as war crimes, genocide and crimes against humanity.
Professor Clark was part of negotiating an amendment to this, known as the Kampala Amendment, which would mean the crime of aggression would fall under the court's jurisdiction.
He said that meant if a state engaged in aggression - crossing another country's border and killing people - the leadership of that country could be jailed under the jurisdiction of the ICC.
Professor Clark said that is exactly what happened to the German and Japanese leadership at the end of World War II, but the Cold War scuppered negotiations for making the crime of aggression a permanent part of international law.
In light of last week's scathing Chilcot report on Britain's decision to go to war in Iraq in 2003 - which the United Nations deemed illegal - Professor Clark said the Kampala Amendment is significant.
"I think if the crime of aggression had been within the jurisdiction of the court in 2003 the United Kingdom government would have been much more reluctant to enter into that."
Green Party MP Kennedy Graham has been pushing for New Zealand to sign up and help to ratify the amendment, and has put forward a private members bill on the matter.
A 2013 Foreign Affairs, Defence and Trade select committee report recommended the government give priority to New Zealand becoming one of the 30 founding states needed to implement it.
But it has not moved forward, and Iceland and Palestine signed up last month making them the last two countries to get to 30.
Professor Clark said major players like Germany and Belgium have signed up and he believed New Zealand was slow off the mark.
"I know they've been thinking seriously about it but I would have expected them to be in the first 30, but I was wrong about that."
Dr Graham said he was disappointed the government had taken so long to act on it since the 2013 recommendation.
"There's been this deathly silence for three years. It's not the simplest thing in the world, but if it's good enough for Liechtenstein and Germany and Switzerland and other countries, major countries and minor countries to ratify, I like to think New Zealand should be up there."
Attorney General Chris Finlayson said the government would make a formal decision on the matter in due course.
"I know that some may wonder why no action has been taken despite the recommendation to the House, well I'd like to think it reaffirms that we're taking the issue very seriously, looking at the issue and MFAT (Ministry of Foreign Affairs and Trade) propose to work with their Minister in the near future to get an answer."
Mr Finlayson said New Zealand officials both here and overseas were following international developments closely and were undertaking the necessary steps to enable the government to make a formal decision in the near future.