Populist politicians are quick to promise solutions to everyone's problems, but often fail to deliver. Just look at Brexit and the election of Donald Trump. In the UK, the nationalists who campaigned so hard for Britain to turn its back on Europe promised that Brexit would mean Britain could trade more easily with the world. More money would be available for healthcare, food prices will come down and the "ordinary, hardworking people will benefit". But many of these promises were immediately dropped within a few days. Independent economic forecasts now suggest Brexit will hit those people least able to afford it.
Likewise, in the United States, the new President-elect Donald Trump promised many changes on the campaign trail, but already many of these have faltered. By cancelling the trans-pacific partnership deal, Trump will only vacate space for China to step in and increase its influence in Asia. Will this really bring jobs and wealth to de-industrialised areas in the mid-west of the US?
We must listen to people's concerns about globalisation, but the response should not be protectionism, but rather to shape globalisation so that it works for us. Free trade should be defended - but it must be fair trade. The European Union has the power to shape globalisation and we should harness it. One of the greatest delusions spread by populists on both the left and right is that turning inwards will empower us. The reality is that in an inter-connected world, no one European country can influence global trade rules. And make no mistake: if we abandon shaping the environment around us, others will shape us.
This is why internationalism is so important; far from diluting national influence and control, pooling sovereignty actually helps to leverage more control and influence on the world stage. Populists who shout, "we want our country back" and "let's take back control" are doing so as they give up power. Another example of how internationalism and the pooling of sovereignty has benefitted us all is Nato. In light of the election of Trump- we can no longer fully rely on the US to protect us, so it makes sense for the EU to finally do much more to share military procurement and progressively integrate its military forces.
As well as providing security for its citizens, we need an EU that defend its values too. Many populist Conservative parties across Europe are abandoning their moral principles in the pursuit of power. When the simple and exaggerated promises made by right wing populists fail to materialise, there is always someone else to blame. In Poland and Hungary, we have seen politicians attacking the judiciary. Our liberal democratic institutions should be defended at all costs.
It is clear to us that if the EU is to survive; the people are going to have to fight for it.
There is nothing patriotic about unjustified attacks by desperate politicians on a national constitution. Modernisers should be clear that the European Union needs radical reform and be honest; the EU of today doesn't work as well as it should. But at same time, we know that if the EU didn't exist, it would have to be created, so the principles underlying the European Union should be defended. After all - we could well be one or two national elections away from the disintegration of the EU. Let's try and fix it, not throw it away.
Russia is actively chipping away at the West's democratic heritage, by spreading misinformation and funding far right ideologies across Europe. Let's confront this. The US played a historic role in supporting the European Union after the second world war, yet senior figures advising Donald Trump now openly promote the breakup of the EU. It is clear to us that if the EU is to survive; the people are going to have to fight for it.
Liberal Democratic, centrist parties must unite and lead this battle. We will do so because we are internationalists, not protectionists, we believe in fighting for societies where everyone is treated with respect, every voice is listened too, rather than the divisive "us v them" rhetoric deployed by many populist parties. We will tackle the populists head on, because not only do they seek to divide, they make empty promises they cannot possibly deliver and then threaten western liberal democratic values when they fail. Together let's move Europe forward and ensure it works for everyone.
Guy Verhofstadt is President of the Alliance of Liberals and Democrats in Europe, and a former prime minister of Belgium
Ryszard Petru is leader of Poland's Modern Party (Nowoczesna)