Australia’s prime minister has the power to launch a war. The almost unfettered right to take the nation into conflict is a stark and simple statement about our system and our history of wars.

The ‘almost’ bit of ‘almost unfettered’ is a small modifier.

A prime minister in command of his or her cabinet and with a majority in the House of Representatives faces no fetters.

The wars change, but the Australian way to war hasn’t changed in a century.

The prime minister declares the deployment or announces the conflict and the troops march and the ships sail. This is the leader’s most profound prerogative.

The PM confident of cabinet and party can act without any authorisation or resolution from the parliament.

Parliament is the stage for high drama, fine speeches, arguments of great political import, and eventually budget authorisation. But in that first, monumental choice, the prime minister and cabinet have ‘comprehensive discretion’ in defence of the Commonwealth. The comprehensive discretion line is from Robert Menzies, writing in 1918 as a Melbourne law student.

Menzies’s article is the starting point for one of the excellent papers by Australian researcher Peter Mulherin on war-power reform in Australia. Mulherin observes that ‘it remains the executive’s “melancholy duty to inform”, rather than consult, on when Australia will next be going to war’. ‘Melancholy duty’ is the famous phrase from Menzies’s broadcast to Australians in September 1939 informing them that Australia was at war.

Surveying the role of parliament in Australian foreign policy 40 years ago, a smart Liberal senator (John Knight) and a fine historian (W.J. Hudson) pointed out what an unhinged prime minister could do with the profound prerogative. The ‘marvellous freedom of executive government in external policy’ meant a deranged PM had the power to declare war simultaneously on the United States and the Soviet Union, thus bringing ruin and destruction on Australia and its people. By contrast, if the same leader wanted to add a cent in tax to the cost of cigarettes, he or she would face a long legislative trek through the parliament.

The agonies and failures in Vietnam and Iraq have caused much soul-searching about giving parliament greater oversight of war power. Draft bills to give parliament a role in sending the Australian Defence Force to serve overseas have been presented in the Senate intermittently since the 1980s. Each time, the parties of government, Labor and Liberal, combine to dismiss the idea.

See how this plays in the 2010 report of the Senate Foreign Affairs, Defence and Trade Legislation Committee on a draft bill from the Greens. The report stressed ‘uncertainty and confusion around the use and application of terms such as war and non-warlike service’ and worried about ‘the nature of the resolution to be agreed to by both Houses of the Parliament’.

Worrying about agreement between the houses (getting the Senate to pass what the government wants) is the shared nightmare of Labor and Liberal prime ministers. Pushing a budget through the upper house is annual purgatory. Imagine trying to get the Senate to approve war.

The parties of government strut and rule in the House of Representatives. Rarely commanding a majority in the Senate, the same parties must go into bargain-and-beg mode. Many government dreams die in the upper house.

So any effort at a greater parliamentary role in deciding to go to war must centre on the House of Representatives. Even that more limited vision crashes against the Labor–Liberal unity ticket to maintain their prerogatives when in power.

One coming milestone of history, plus voting trends confronting the parties of government, will push against the prime minister’s prerogative.

The milestone will be the release under the 20-year rule of the cabinet archives showing how the Howard government decided to go to war in Iraq in 2003. The archive vault will be opened and what will be there? Almost zilch.

When the cabinet papers for 2003 are released by the National Archives of Australia on 1 January 2024 there’ll be an extraordinary absence. I’ve called this the Canberra silence on Iraq. John Howard didn’t ask the bureaucracy to produce a paper on the central issue of war. The cabinet submission arguing the pros and cons of war doesn’t exist.

The absence of those arguments for war and what the war would mean is one of those big topics that quickly entered Canberra’s lore. A prime minister driving Australia to an unpopular war didn’t want any official thinking that would trouble his cabinet, roil his party, and cause great public damage when it invariably leaked.

The revelation of that Canberra silence will generate headlines for a day and fascinate the historians.

The big trend with future impact is the slow change in the workings of Australia’s two-party system and the erosion of the primary vote for Labor and the Liberal–National Coalition.

In the 20th century, the roughest of rules proclaimed that Labor and the Coalition each got around 45% of the primary vote in the House of Reps. Then the distribution of preferences gave government to Labor or the Coalition.

This century, the 45% rule is broken. Instead, today’s rough guide is the 33% standard for the lower house primary vote—one-third for Labor, one-third for the Coalition and one-third for independents and the Greens.

The preference system no longer has that simple binary effect in delivering for the parties of government. The one-third guide slowly seeps into the system and eats at the simplicities of the Labor–Liberal binary. So far this century, Australia has had only one minority government. But the atomisation of the vote has set in.

The trend will make it harder for governments (the executive) to strut and rule in the House. And a parliament with more ability to check the prime minister’s power will come eventually to that profound prerogative in the Australian way of war.