The key to determining the direction of the Conservative party lies with its leaders and the best way of understanding Conservative divisions is probably via them. Unlike its main rivals, the Conservatives are driven to an extraordinary degree by the men and women who lead it. While Conservative grassroots members are broadly right-wing, often putting them at odds with more liberal minded leaders, they are also fundamentally loyal. They do not have pretensions to directing the parliamentary party, even if they now expect a say in how it is led (although such a say is rare - only Iain Duncan Smith and David Cameron became leaders as a result of a grassroots vote).
Party historians date the Conservative Party back to either Robert Peel or William Pitt the Younger. Pitt embodied the free trade philosophy that has remained part of the party's policy DNA (leading to a substantial internal divide at the beginning of the twentieth century) while Peel was an early social reformer. Peel's cabinet included William Gladstone while his backbench MPs included Benjamin Disraeli. Gladstone took his economic liberalism to the Liberal Party after the repeal of the Corn Laws split the party, while Disraeli eventually came to articulate what he called a One Nation vision for the Conservatives.
One Nation Conservatism - a somewhat inchoate, pragmatic blend of paternalism and specific government action to benefit the working poor in the interests of national harmony - came to dominate the Conservative Party for much of the twentieth century. However, it was encountering problems under Edward Heath and it fell to Margaret Thatcher to provide something hitherto unknown for Conservatism - an ideology. The liberal conservative Ian Gilmour had noted that "the wise Conservative travels light" but such lightness of travel wasn't benefiting them by the 70s, so Mrs. Thatcher brought back a form of Gladstonian liberalism in economic thought - essentially a promulgation of the virtues of the free market and private ownership - and married it with traditional Tory social conservatism.
Whilst opposed by liberal, or One Nation, Conservatives such as Gilmour on account of its negative impact upon working class communities (notably miners and traditional manufacturing workers), Thatcherism became the dominant Conservative ideology in the latter part of the 20th century. Economic liberalism, in the form of a small state, low tax vision, was not seriously questioned although social attitudes did become a battleground between liberals and conservatives.
David Cameron became leader in 2005 and sought to modernise the Conservative brand without seriously changing its policies. He coined the term "Big Society" for his 2010 election manifesto (an updated version of One Nation Conservatism), though in practice this amounted to little specific in terms of policy. He also sought to focus more on 'Green" issues and social liberalism to soften the Conservative image; his embrace of gay marriage was a success for social liberals but put him at odds with a still significant socially conservative membership of his party. He pursued some further devolution of powers away from Westminster, to a proposed "Northern Powerhouse" (the hobbyhorse of his key ally and Chancellor George Osborne) and the metro mayors elected last May - a lingering legacy. There was also a feeling that his desire for a formal coalition with the Liberal Democrats was in part motivated by a need to have a liberal firewall against his own more right-wing back-benchers. In government, however, he and Osborne found themselves nonetheless pursuing an austerity agenda in the light of the 2008 financial crisis that wouldn't have looked out of place under Mrs. Thatcher herself.
Like all Conservative leaders since Thatcher, Cameron was faced with a Europe problem, which he resolved by promising a referendum. He can hardly have foreseen that this referendum would spell his own precipitate political end just a year after winning an independent majority for his party in the 2015 election.
And so we come to Theresa May. Her speech on taking office seemed to mark the outlines of a form of One Nation Conservatism, and the 2017 Conservative manifesto - which more than many of its predecessors is the work of the leader's small coterie, notably co chief-of-staff Nick Timothy - seems to have embedded this further. Characterised by some as "Red Toryism", May's manifesto actively promotes the idea that the state can be used to further the public good. It talks of the "good that government can do" and rejects what it calls "the cult of selfish individualism". It wants public schools to set up state academies, promises to maintain the workers' rights that are currently embedded in EU law and even rejects the idea of ideology as "dangerous".
In her determination to use the state to protect workers and provide government oversight of businesses, May echoes some of the activist agenda of Disraeli (or more accurately his Home Secretary Richard Cross). In identifying herself as the emblem of conservatism and thus the nation, the only person trusted to negotiate our exit from the European Union, there are echoes of Stanley Baldwin's "Safety First" agenda in the 1930s, although they lack his sense of ease at the state of the country.
In the modern age of an expansive state, however, which has often been the target of Conservative determinations to reduce it, May has also arguably carved out a new brand of Conservatism. One which seeks to utilise the state rather than attack it, and do so in order to widen the appeal of 21st century Conservatism to those who are not people of wealth or rank. The so-called "just about managing" that she identified in her first speech. Shorn of the Brexit veneer, she could be seen as the most left-wing Conservative premier yet. This is why a High Tory like historian Andrew Roberts is so worried, as he argues in this piece, suggesting that she is not really a Tory at all.
The Conservatives are the most pragmatic and flexible of democratic political parties. It is one reason why they are still in business after more than two centuries. How long lasting the May changes will be are of course dependent on the level of endorsement she gets from the electorate, and a couple of weeks before the election itself that isn't looking quite so rosy.