In 10 days’ time, two political dramas will reach their denouement, thanks to the votes of a combined total of about 1.3 billion people. At the heart of both will be a mess of questions about democracy in the online age, and how – or even if – we can act to preserve it.

Elections to the European parliament will begin on 23 May, and offer an illuminating test of the rightwing populism that has swept across the continent. In the UK, they will mark the decisive arrival of Nigel Farage’s Brexit party, whose packed rallies are serving notice of a politics brimming with bile and rage, masterminded by people with plenty of campaigning nous. The same day will see the result of the Indian election, a watershed moment for the ruling Hindu nationalist prime minister, Narendra Modi, and his Bharatiya Janata party, or BJP. Whatever the outcomes, both contests will highlight something inescapable: that the politics of polarisation, anger and what political cliche calls “fake news” is going to be around for a long time to come.

WhatsApp has more than 300 million Indian users, and it is Modi and his supporters who have made the most of it

In Facebook’s European headquarters in Dublin, journalists have been shown the alleged wonders of the “war room” where staff are charged with monitoring European campaigning – in 24 languages – and somehow minimising hate speech and misinformation put around by “bad actors”. But this is as nothing compared with what is afoot in the world’s largest democracy, and a story centred on WhatsApp, the platform Mark Zuckerberg’s company acquired in 2014 for $22bn, whose messages are end-to-end encrypted and thus beyond the reach of would-be moderators. WhatsApp is thought to have more than 300 million Indian users, and though it is central to political campaigning on all sides, it is Modi and his supporters who have made the most of it. The political aspects of this blur into incidents of murder and violence traced to rumours spread via WhatsApp groups – last week, the Financial Times quoted one Indian political source claiming that WhatsApp was “the echo chamber of all unmitigated lies, fakes and crap in India”.

When I spoke to the UK-based Indian academic Indrajit Roy last week he acknowledged India’s “dangerous discourse” but emphasised how the online world had given a voice to people who were once outsiders. He talked about small, regional parties live-streaming rallies in “remote parts of north India”; memes that satirised “how idiotic and self-obsessed [Modi] is”; and people using the internet to loudly ask why India’s caste hierarchies held them back so much. But then came the flipside. In that context, he said, it was perhaps not surprising that Modi was now leading “an elite revolt against the kind of advances that have happened in the past five or six decades, whether it’s the rights of minorities, so-called lower castes, or women”. The fact that he and the BJP are using the most modern means of communication to do so is an irony evident in the rise of conservatives and nationalists just about everywhere.

This, then, is an Indian story, but it chimes with what is happening all over the planet. With the help of as many as 900,000 WhatsApp activists, the BJP has reportedly collected reams of detailed data about individual voters and used it to precisely target messages through innumerable WhatsApp groups. A huge and belligerent online community known as the Internet Hindus maintains a shrill conversation about the things that its members think are standing in the way of their utopia: Muslims, “libtards”, secularists. There are highly charged online arguments about Indian history, often led by the kind of propagandists who never stand for office and thus put themselves beyond any accountability. Thanks to the Indian equivalent of birtherism, there are also claims that the Nehru-Gandhi family, who still dominate the opposition Congress party, have been secret followers of Islam, a claim made with the aid of fake family trees and doctored photographs.

Facebook Twitter Pinterest Indians wait to cast their votes in New Delhi on 12 May. Photograph: Manish Swarup/AP

Partly because forwarded messages contain no information about their original source, it is by no means clear where the division between formal party messaging and unauthorised material lies, so Modi and his people have complete deniability. They benefit, moreover, from the way that the online world seems to ensure that everything is ramped up and divided. To quote Subir Sinha, an Indian analyst of society and politics based at London’s School of African and Oriental Studies: ”You can’t just be a nationalist; you’ve got to be an ultra-nationalist. You can’t just be upset by Pakistan’s actions; you’ve got to be outraged.” He calls this “hyper-politics”, and says that its international lines of communication have led some to some remarkable things. “Tommy Robinson is extremely popular among Modi supporters,” he told me. “You will find mega-influencers of the Indian right who will approvingly post Tommy Robinson material in WhatsApp groups, or on Twitter.”

Yes, the internet is still replete with possibilities of emancipation and pluralism, but herein lie the basic features of the global 21st century: disagreements that have always been there in politics, both democratic and otherwise, now seem to have been rendered unstoppable by technology. Significant parts of society are kept in a constant state of tension and polarisation, a state exacerbated by the algorithms that privilege outrage over nuance, and platforms that threaten to be ungovernable. Though the old-fashioned media maintains the pretence that electioneering is the preserve of parties, campaigns around elections (and referendums) are actually loose and open-ended – often mired in hate and division and full of allegations of corruption and betrayal. We are seeing the constant hardening-up of political tribes – religious communities, liberals, conservatives, nationalists, socialists, cults built around supposedly charismatic leaders – with victory going to the forces that can most successfully manipulate the online ferment.

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Modi is a dab hand at this. So are the forces behind the Brazilian president, Jair Bolsonaro. Important Brexiteers are expert in the same techniques; as evidenced by his Twitter presidency, the same is true of Donald Trump. On the left, too, there are clear manifestations of a politics transformed by the way we now communicate – not least in and around Corbynism, which represents both sides of the new reality: simultaneously the most serious threat to established thinking for decades and a long-overdue push against inequality and the lunacies of the free market, and also the focus of a shrill, all-or-nothing, sometimes truth-bending online discourse.

Whether the platforms at the heart of this new world might eventually start to get to grips with the downsides of what they have created is a question obscured at present by unconvincing half-measures, and the kind of flimsy PR embodied by a recent WhatsApp advertising campaign that encouraged its users in India to “Share joy, not rumours”.

The reality of where we are headed was perhaps highlighted only a few months ago, when Zuckerberg announced a new vision for Facebook, built around the mantra “The future is private”, and a proposal to make his most successful invention much more like WhatsApp – an attempt, as some people saw it, to start a journey towards Facebook having no responsibility for the content of its networks because encryption would render everything conveniently impenetrable. In that sense, the Indian experience may not be any kind of outlier but a pointer to all our futures. If that turns out to be true, what are we going to do about it?

• John Harris is a Guardian columnist