Editor's Note: (Guy Verhofstadt, a former Belgian prime minister, is president of the Alliance of Liberals and Democrats for Europe Group (ALDE) in the European Parliament. The opinions in this article are those of the author.)
(CNN) Next year's European elections could arguably be the most significant in the short history of the European Union.
In the wake of President Trump's victory in the United States and the Brexit referendum, we are seeing the polarization of politics on the European continent.
Right-wing populists and nationalists, led by Hungarian Prime Minister Viktor Orbán, are squaring off against those who want to defend liberal democracy and fight for an open society.
During a recent meeting with the leader of Italy's far-right Lega party, Matteo Salvini, Orbán declared: "There are two sides at the moment in Europe. One is led by Macron, who is supporting migration. The other one is supported by countries that want to protect their borders." French President Emmanuel Macron hit back: "If they want to see me as their main opponent, they are right."
With the backing of alt-right leader Steve Bannon and the blessing of Russian President Vladimir Putin, the far right's plan is to spread the populism that delivered Brexit and Trump to provoke an implosion of the European project and an erosion of the democratic institutions the US has helped to develop since the Second World War.
In the absence of traditional support from the US administration, it rests with pro-Europeans and defenders of liberal democracy in Europe to challenge head-on the myths and disinformation perpetuated by populists.
For too long, in both the US and Europe, populists have gotten away with selling a retreat to isolationism and protectionism, wrapped up in a rose-tinted notion of absolute national sovereignty, as a solution to voter's problems. Progressive voices must now challenge these assumptions and once again make the case for internationalism.
Nationalists worship at the altar of the nation state, but in 2018 it's obvious that no European country can tackle climate change, people trafficking or drug smuggling on its own.
Pooling some sovereignty to better shape the world around us does not mean giving away control -- it is a means to leverage power and take back control in a world increasingly dominated by social media companies and tech giants.
If the US or Europe does not shape the rules of international trade, China will. If we do not act to define limits on artificial intelligence, we leave that power to companies like Amazon or Google.
Likewise, with migration, no single European country can deliver a fair and humane system that would work in practice. Far-right European populists like Salvini and Orbán have successfully exploited people's fears about migration by turning Europe's refugee crisis of 2015 into a political crisis.
Yet in many instances, in both the US and Europe, fears over migration are based on perceptions of the number of immigrants in our societies, rather than the actual numbers: a feeling, as opposed to reality.
Migration is central to the human story, but progressive politicians must also offer real solutions to people's concerns. In Europe, liberals and democrats must show it is possible to build a collective, humane asylum and migration system founded on a respect for our international obligations. This must come hand in hand with a more responsible and coherent foreign policy.
Just as Europeans failed to adequately respond to the global financial crisis, the West's failure to stop Putin and Assad's bloodshed in Syria and the collapse of Libya are all drivers of Europe's migration challenges, now used by the far right to undermine liberal democratic parties.
A credible and serious European foreign policy, backed up with a joint European defense capability, could change this dynamic. American friends of Europe should be bold in pressing for EU reform.
To prevent a victory for Steve Bannon and his ragbag of right-wing populists in next year's elections, it falls to pro-Europeans to offer a vision of hope and renewal: a promise to deliver enhanced rights and freedoms for all the citizens of Europe.
Such a program would stand in stark contrast to the dystopian offer of "unfreedom" promised by the far right.
The new divide in European politics is not between left and right, it is between nationalist illiberalism and pro-European liberal democracy. We face a battle for the defense of liberal democracy and the stakes are high.
Europeans and Americans who value a democratic and peaceful European continent must start tackling the lies of right-wing populists head-on, while offering a positive alternative vision of a democratic, outward-looking, reformed European Union at peace with itself.