The Labour Party has always been split over foreign policy. The Boer War, fought between capitalists and racists, made it difficult to choose a side; likewise the First World War (imperialism v. Prussianism); less so the Second World War, which divided the Conservatives more. The Falklands War was fought against a fascist dictator, but by the hated Thatcher and in defence of a colonial relic. And then there's the Iraq War and the bombing of Syria.

All these conflicts have posed genuine moral quandaries for ‘progressives’, which is why they have been so damaging for party unity. Suspicious leftists have occasionally wondered whether they might not have been deliberately provoked by the right in order to have this effect, an idea that goes back to the mid-Victorian Liberal Richard Cobden. It seems unlikely, though Thatcher and Cameron have obviously been aware of the benefit for them. Such divisions are natural and even commendable, and should not be wondered at, especially in a party that originated in a desire for domestic economic and social reform. But they are unfortunate for Labour in a political climate – inside the Westminster ‘bubble’, at any rate – in which discipline appears to be rated higher than democracy. Without the divisions over foreign policy, it seems likely that the party could pretty well unite on most of the big domestic issues of the day: equality, the role of the state, anti-austerity, even immigration; leaving it free to oppose its main enemy – a government intent on pushing through hugely divisive right-wing policies with the support of only a quarter of the electorate – much more effectively.

This problem seems to be largely absent in most other European countries, where disputes over foreign policy are less likely to affect broad democratic decision-making. This must be a relic of Britain’s old imperial role, which gave it the idea that it ought to involve itself in other nations’ affairs, for whatever reasons, aggressive, defensive or humanitarian; and then prolonged that supposed duty long after its sell-by date. France also retains some of this. Germany was cured of it, at least for the time being, by the result of the Second World War. Progressive politics in Britain, however, are still beleaguered by it, unnecessarily. In democratic terms there is no reason why a party broadly united on domestic issues should not embrace diversity on foreign policy, and still be effective domestically. The Conservatives seem to be managing, with all their equally profound divisions over Europe.