Imagine for a moment that Emmanuel Macron had left the retirement age well alone. In this other France, the president chose to economise on defence instead. Fewer troops. Humbler ambitions in the Pacific. A budget nearer 1 than 2 per cent of national output.

Would the republic now be aflame with protests? There would be hurt pride, no doubt. Michel Houellebecq would get a didactic novel out of it called something like Impuissance. But who thinks France would be so tense as to be unvisitable by the monarch of an allied state? It is beyond imagining. Take the nation’s guns, if you must, voters would say. Just don’t touch the butter. And this is France, with its martial pedigree, its militarised Bastille Day. If a culture so steeped in hard power prefers civilian spending, what will the average nation choose?

To counter Russia and China, the most important democracies in the world are arming. The decision has come from governments of the right (Britain), the left (Germany) and the hard to place (France). It comes from the best-armed nation in history (the US) and one that is constitutionally pacifist (Japan). Such is the breadth of consensus that even Sweden has stopped telling the polite lie that soft power and moral example-setting are enough. The leadership on show is first-class. It is, in truth, overdue. I just wonder if these electorates are good for the money.

It is excruciatingly difficult in a mature democracy to make even marginal cuts to the welfare state. It is about as hard to sell the public on a net increase in taxation. (France has almost the highest tax burden in the OECD. The gilets jaunes rose up, at first, against fuel levies.) What the past year has done is turn this dilemma into a trilemma. A third goal, that of stronger defence, has joined the two irreconcilables. Something will have to fall away here, and the historical trend suggests which it will be.

Conservatives are wrong to accuse the west of turning from defence to welfare when the Soviet threat vanished. No, the problem is much older than that. In Britain, “defence cuts effectively paid for a growing welfare state for 60 years,” wrote Ben Zaranko of the Institute for Fiscal Studies in 2022. Ronald Reagan is now seen as near-Prussian in his militarism. But defence spending nearly halved as a share of national output between the presidency of Dwight Eisenhower and the peak of his own.

In other words, the peace dividend was being cashed long before 1989. Some of this redistribution from soldier to civilian was wise. The home front needed tending. After the Cuban missile crisis, the cold war had got past its hairiest phase. But the sheer duration of this trend augurs badly for the chances of its reversal now. If the west is going to go on a generational spree in defence, it will have to undo the habit of a human lifetime, not just of the past 30 or so years. Voters will have to make economies for a defence sector that is more remote and obscure to them than it was the mid-20th century, when conscription made it hard to tell where the military ended and civil society began.

The choice between guns and butter, defence lobbyists will say, isn’t as clean as all that. The US military is a kind of auxiliary welfare state, providing employment, housing, medical coverage, college aid and childcare to citizens who might otherwise go without some or all of these things. Poor states would be poorer without defence or defence-adjacent jobs. Imagine Alabama minus Maxwell Air Force Base or the contractors at Huntsville. In Britain, the only “levelling up” plan that doesn’t strike me as utter pie in the sky is one that uses an enhanced defence budget to spread research and manufacturing work to deindustrialised regions.

At the margins, then, the relationship between defence and welfare is circular. More often, though, it is oppositional. Governments have to decide between a retirement age here and a naval fleet there.

Or rather, voters do. If they go the way I fear, it will be a legitimate and understandable democratic choice. But then so was the inward turn of the interwar years. The second world war happened, in part, because Germany and Japan didn’t believe a US that had let its hard power run down for a generation could counter them. (To re-militarise took the Americans what Churchill called a “prodigy of organisation”.)

It is to avoid sending the same signal to their contemporary enemies that democracies are arming now. To judge by the chaos in Paris, financing this vision of deterrence will be harder than setting it out. Weakness is provocative, goes the cliché. But so, at home, is paying for strength.

janan.ganesh@ft.com