Despite Jeremy Corbyn’s surprising appearance at the Progress annual conference on Saturday, unity is proving difficult to achieve in the Labour Party.

Why is this, in a party that, whilst it is famous for factional schisms and personal antipathies between leading politicians, is also known to be very sentimental about supporting whoever is the incumbent leader?

Corbyn’s model of leadership is not the norm. If you look at Labour Party history since 1931 almost all leaders have followed a “party management” approach, presenting themselves as a consensus-builder, above and balancing and reconciling factional manoeuvring by the senior shadow cabinet members below them, and seeking to find a way forward for the party that was acceptable to a very broad sweep of party opinion. This was the model of leadership practiced by Attlee, Wilson, Callaghan, Foot, Kinnock, Smith, Brown and Miliband. The only leaders Labour has had since 1931 who sought to challenge the party and take it on a sharply ideological path in a direction that might be unpalatable to a large section of party opinion were Gaitskell and Blair who both advocated forceful revisionist modernisation, and Lansbury and Corbyn seeking a return to a more leftwing vision.

Given that the norm is for leaders to be primarily concerned with unity and managing different strands of opinion in the party by finding a consensus it is unsurprising that when a leader provokes one part of party opinion with a sharp change of political direction, this creates disunity. You can’t expect senior elected politicians to just follow in a direction that they have fundamental moral or strategic disagreements with.

Trying to fundamentally shift the direction of a big political party with all kinds of interest groups in it is a high risk strategy.

Lansbury’s efforts to take the party leftwards ended in humiliation at the hands of TGWU leader Ernie Bevin over appeasement of Mussolini. Bevin told Lansbury at conference “It is placing the Executive and the Movement in an absolutely wrong position to be hawking your conscience around from body to body asking to be told what to do with it”, precipitating Lansbury’s resignation.

Gaitskell’s efforts to move the party to the centre had an equally rocky journey, with him having to drop entirely his proposal to change Clause IV’s commitment to state ownership, and initially losing the key vote at annual conference on multilateral disarmament and having to come back a year later after expending much effort organising in the CLPs and unions. He even faced a direct leadership challenge from Harold Wilson in 1960, with 81 MPs voting Wilson versus 166 for Gaitskell. Wilson ran on a platform of “unity versus civil war”. Gaitskell’s premature death means we don’t know if his project would have succeeded.

The only leader who did succeed in a fundamental shift in direction of the party was Blair. He came into office in unique circumstances which made such a shift palatable. Four general election defeats meant party members as well as MPs were prepared to accept changes they might not have personally agreed with, like the new Clause IV, as necessary to finally beating the Tories. And the two previous leaders, Kinnock and Smith, whilst nearer to the centre of gravity of the party, had already done a lot of the organisational spade work Blair needed for his revolution, expelling Militant, ditching unilateralism, and introducing One Member One Vote. If changing Labour’s direction is like turning a huge oil tanker, Kinnock and Smith had already been holding the tiller to starboard and executing a long slow turn for 11 years before Blair even arrived on the bridge.

Blair found that nothing succeeds like success and was able to get away with a decade of moving Labour further and further from its comfort zone because MPs in marginal seats knew they owed their political careers to his decisions and his uncanny empathy with swing voters, even if in their hearts it wasn’t the direction they all wanted to go in. He only came unstuck when alienation of key groups of voters due to the Iraq War and tuition fees meant that an alternative more consensual approach from Brown looked like it might be more electorally popular.

Like Blair, Corbyn inherits a party willing to try a dramatic change of direction to get out of a long run of defeats.

He also inherits a situation where Ed Miliband had been the epitome of the unity leader model, anxious to manage divisions in the party, and had ended up with a kind of lowest common denominator manifesto that tried to please everyone but enthused no one, thus opening up an argument for his successor to be someone more radical.

But there is no obvious electoral territory to conquer in the leftwards direction Corbyn is taking us in. Whilst the election results on 5 May were mixed, they did not suggest that huge pools of SNP voters and disillusioned non-voters waiting for a more leftwing Labour Party exist. We’ve got even stronger in the demographics Miliband got stronger in, university towns and core cities, and even weaker in the Con vs Lab swing seats Ed had already got weaker in, which happen to be where General Elections are won and lost.

If there are not obvious electoral dividends, it is difficult to expect MPs to support a strategy that might lead to them losing their jobs. MPs in safe seats can afford to opt for a quiet life of avoiding confrontation with their leader or activists if it means they will still be MPs after 2020 and things might eventually change. But MPs in knife-edge marginal believe they will personally be replaced by Tories in 2020 if the leader doesn’t reach out to the centre ground, hence the preparedness to incur the wrath of the grassroots from Corbyn critics like Ian Austin, John Woodcock, Wes Streeting and most recently Peter Kyle.

Also detrimental to unity has been the approach of Corbyn’s own office and the Momentum faction.

The sacking of Michael Dugher from the Shadow Cabinet and Pat McFadden from the frontbench created two powerful and media savvy voices with nothing to lose, but also sent a message to the group of moderate MPs – who had decided to serve as frontbenchers in order to obtain policy concessions, keep the party afloat and make Corbyn’s leadership work – that there was no point as they would all get purged at some point.

The pushing of policy positions known to be red lines for moderates, such as Trident abolition, has also been detrimental to unity, as most MPs were actually fairly relaxed about Corbyn’s domestic agenda. With a few exceptions, no Labour MP has a huge in principle objection to anti-austerity economics, even if they doubt its electoral popularity, but the Trident debate looks like an attempt to force an unnecessary fight on something a number of MPs and unions just aren’t prepared to compromise on because it is either part of their political identity or of huge industrial importance to the people they represent.

And Momentum has looked like an organisation set up for a fight. Don’t underestimate the amount of good will towards Jeremy and his mandate that has been squandered by social media trolling of even soft left MPs, labelling of diehard Labourites as “Tories”, casual threats of deselection, packing of meetings, disrespect of long-standing activists and volunteer party officers. Threats have a certain traction in crude transactional politics but if it’s all stick and no carrot – if Momentum is going to sweep you aside as an old guard MP, councillor or CLP officer however much you appease them – you are left with no choice but to stand and fight.

We might achieve unity under Jeremy. But the historical precedents and the damage done by early decisions by his supporters make this unlikely.

And if the Lansbury to Attlee, Gaitskell to Wilson, and Blair to Brown transitions are anything to go by, the party only has the stomach for this kind of turmoil for a few years, and Jeremy’s successor is likely to be someone who promises, as Wilson did “unity versus civil war”.