New Zealand has blazed a trail in many areas – not least in opening up its economy to the rest of the world. In the 1980s reforming Labour governments axed the thicket of protectionist tariffs and subsidies that penalised consumers and cossetted – but ultimately held back – Kiwi farmers.

By throwing open the economy to global competition and foreign investment, they started a trend for what is now known as globalisation: the huge – and hugely enriching – expansion of international exchange of goods, services, people, money and data that has brought the world ever closer together in recent decades. Until now?

Until recently, many people thought – wrongly – that globalisation was a technological inevitability. After all, the internet can’t be uninvented. But it can be restricted: witness the Great Firewall of China. And new regulatory moves in Europe and America could gum up data flows more generally.

The biggest threat to our (mostly) open world comes from the revival of nationalism, notably in the United States. In the name of putting “America First”, President Donald Trump seems intent on starting a global trade war, clamping down on foreign investment and building a border wall with Mexico. More broadly, he wants to sabotage the international rules and institutions that underpin open markets – notably the World Trade Organisation, where I once worked as special adviser to its then Director-General, former New Zealand prime minister Mike Moore.

The big danger, then, is that the world is about to repeat the mistakes of the Great Depression of the 1930s, when a protectionist spiral destroyed an earlier era of globalisation. Or less dramatically, that globalisation will be throttled by a thousand small restrictions.

The good news is that for now most countries seem intent on keeping markets open. While Trump pulled the US out of the Trans-Pacific Partnership (TPP), a free-trade deal with New Zealand and ten other Pacific countries, the remaining 11 are going ahead with the agreement without the US.

A broader Asian deal championed by China, the Regional Comprehensive Economic Partnership, has new momentum. And the European Union is pressing on with trade deals with a host of countries, including Australia and New Zealand.

But there is no room for complacency. Nationalism is on the rise in many countries. Winston Peters is not Donald Trump, but it is still troubling that the acting prime minister of this country hails from a party called New Zealand First.

Come to my upcoming talks in Auckland and Wellington – or watch them online – to debate what we need to do to keep our world open.