Thirty years ago, on a momentous November day in 1989 the very first Berliners were able to cross the wall that had for 28 years divided their beloved city.

I don’t think that in modern history, there is any more powerful symbol of division and coming together than the day the Berlin Wall was brought down. Families, friends and lovers reunited.

I was only nine years old when this happened, and like many others my age I hadn’t given much thought to the perils of the Cold War we were living through. In my home in Milngavie, a lovely suburb of Glasgow, with my sister and my parents, it all seemed rather far away.

But I do remember one Saturday morning quite well. I was in our living room, watching Going Live!, the Saturday morning children’s TV show. That particular morning, there was an amazing competition and the prize was to win a piece of the Berlin Wall. My dad must have sensed my disappointment at not winning it, because when he visited Berlin later on, he brought me back a little piece of that history. It is one of my most prized possessions.

That moment thirty years ago was so much bigger than what it meant for the city of Berlin. The wall was going, and with it, the anxiety of two superpowers constantly on the brink of war. The world would be a little safer, a little more prosperous and we would pave the way for liberal internationalism – a system built on the values of openness, multilateralism and cooperation with a set of international rules to help countries engage with each other properly, safely and fairly. These are the values that underpinned the new order, even if we all know that they were not always adhered to.

As a liberal, I believe that these values are more important today than ever. But just as we prepare to mark thirty years of the fall of the Berlin Wall, I am dismayed that so many of our political leaders are intent on building new ones – whether it’s Trump building a physical wall or our country turning its back on our closest allies.

In the rise of populism that we are witnessing here, in the US, and across other parts of the world, liberals are not without blame. As the world prospered thanks to new trade links and advances in technology, we neglected the many back at home for whom life got that bit harder and who watched the top 1 per cent reap many of the rewards of globalisation. And the likes of Trump, Farage and others have taken advantage of the situation and sold a compelling narrative to get votes.

But our response cannot just be to tell people that they’re wrong for voting for strongmen who spout hate and division and stoke fears about foreigners. We have lost the art of disagreeing well, and instead of trying to change the hearts and minds of those who disagree with us, we are far too quick to dismiss them. And to win the argument, liberals have to offer an alternative because just saying no isn’t enough.

At least part of that alternative story is about what we do at home and how we restore confidence in liberalism. The 2008 financial crisis was a huge opportunity to fundamentally change the system that for a growing number of families in the UK is broken. But, in the rush to save the economy, we went back to business as usual. I believe that the technological revolution right in front of us is a second chance that we absolutely cannot waste.

It’s an opportunity to question whether we are measuring progress in the right way and if our obsession with GDP above all else does more damage to our wellbeing and our planet than good. We should ask whether we are properly valuing the things that really matter in our society and why for example we are pursuing further cuts to the rate of corporation tax while we underpay carers who are looking after the most vulnerable in our society.

And we should hold businesses to account because free-riding on the societies in which they operate is not sustainable – they should take responsibility for how their activities affect their employees, their consumers and the environment – none of these things should be sacrificed on the altar of the short-term share price.

When we have found ourselves been at a major crossroads before, it was liberals who found the answers. In the UK, it was liberals who designed the National Health Service, who made education compulsory and who first offered support to the jobless. And when the world was emerging from the horror of another war, it was liberals who put their values into action and achieved 70 years of peace and stability.

At some point over that time though we lost our way: liberal values are on life-support, but I have no doubt that there is life in them yet. Because if there is one thing liberalism can do is adapt, change, reform and reinvent itself. And it is so important that we commit to do just that, both at home and on the international stage, because the challenges we face today – whether it’s climate change, terrorism or cybercrime – are bigger than any one country and only together do we have a chance at beating them.

Jo Swinson MP is deputy leader of the Liberal Democrats and delivered the annual Lord North Commemorative Lecture at Wroxton College