This is a year of birthdays for anyone involved in Europe’s defence. In early April, NATO celebrated the 70th anniversary of its founding document, the Washington Treaty, which set up the most successful security alliance the world has ever seen. And it was forged less than five years after one of the most important military operations ever undertaken: the D-Day landings on June 6, 1944, 75 years ago.

The two are related, of course. The Normandy landings set the scene for the final act of the Second World War in Europe. Some 156,000 American, British, Canadian and other Allies landed that day, the largest amphibious invasion in history. It was the culmination of a year-long plan, conceived by an extraordinary alliance. Even though the aims of the allies were met when the war ended in 1945, the experience of working together helped inform the creation of NATO in 1949.

NATO’s 70th birthday was greeted with wariness from quite a few commentators who asked whether the Atlantic Alliance had served its purpose. They wondered whether it could survive today’s threats, be them from terrorism, a revanchist Russia, an assertive China, or even from a US president demanding that NATO’s European members spend and do more on defence.

But looking back over NATO’s seven decades, threats have always been part of its life. It was born as the western allies faced an existential menace from the then Soviet Union, which loomed ominously until the fall of the Berlin Wall in 1989. Terrorism has also always been part of the landscape, as has religious extremism (for example, the 1979 Iranian revolution, and the tensions between India and Pakistan).

NATO’s story covers the Cuban missile crisis, the Cold War near misses in the 1980s, and even the tensions between members Greece and Turkey. NATO endured these challenges from the start. And each time, they have been used to move the alliance forward in some respect, to help to grow new tissue, and to thrive.

Some make the point that the founding principles of NATO have changed over the years and that the security demands of 1949 are no longer there. The same, perhaps, could be said about the European Union: the project began as one of reconciliation, but it too has changed. That may well be the case, but the value of NATO – and indeed, the EU – is now almost indisputable. It is one of unity, peace, democracy, and power.

Back in 1949, the military capabilities of the 12 signatories of the North Atlantic Treaty were all separate. The D-Day landings and Operation Overlord brought some of them together for one specific project, which was often improvised. But NATO gathered them in a much more substantial way, notably through interoperability and standardisation.

Speaking from personal experience, I have witnessed many changes since I first entered service in the Dutch Navy more than four decades ago. Many of NATO’s initial efforts at cooperation and harmonisation were in the naval domain, with air forces and ground forces following later. Yet it was only in 1960s that the first time a naval squadron was created under a NATO flag: the Standing Naval Force Atlantic (STANAVFORLANT), a contingency force of destroyers and frigates, providing a high readiness response and day-to-day verification of current NATO maritime procedures, tactics and effectiveness (now known as Standing NATO Maritime Group One, or SNMG1).

NATO is hard work. It takes time, and it covers different domains. It includes shared visions and shared authority. It includes technology, like the Airborne Warning and Control System (AWACS). It includes storage of member countries’ vital equipment in depots across the NATO territories. It includes standardisation not only in material, but in tactics and procedures – like the STANdardization Agreement (STANAG) that defines processes, terms, and conditions for common military or technical procedures or equipment between the member countries of the alliance. Having the NATO structures, including headquarters that brought military and civilians together in a single site, also helps coordinate thinking.

Symbolic acts of reconciliation carry weight. The first time I laid a wreath was as a junior officer at the port of Kiel, at a monument for German submariners. The Second World War was still within living memory for many people, and this was sensitive: I was hesitant about effectively commemorating U-Boats, and thought about all that my parents had endured during the war. But I did it, and the gesture worked. It was followed by a lot of exchanges between the Dutch and German navies that proved vital. This glue allowed us to grow.

I have seen this growth with my own eyes. But I have also sat through the long meetings that made it possible. These might look like painstaking bureaucratic procedures, but they all help ensure that NATO members eventually make a smooth transition to agreed systems. These measures have helped NATO expand from 12 to 29 members, deploy to theatres as far as the Red Sea and Afghanistan, fight cyber threats and terrorism, organise huge training exercises, and develop rapid reaction forces.

In 1949, the clever people behind NATO remembered the lessons from the Second World War. There were many different armies involved in D-Day, and many strong characters, like US Army Chief of Staff George Marshall, Supreme Allied Commander Dwight Eisenhower, US General George Patten, and British General Bernard Montgomery. They all had their identities and their egos. Stitching armies together for a single joint operation was difficult enough. A more enduring alliance would take more time and patience.

Many concerns about the meaning of NATO miss the point that its organic growth is part of its strength. It has evolved its capabilities slowly, for obvious reasons. But it is stronger for its gradual build-up.

NATO needs to continue adapting to ongoing threats over the coming years. And it will need to think creatively as its founding fathers did. Its collective defence is a precious principle, and it has been preserved and strengthened over the years. Both the 70th anniversary of the North Atlantic Treaty and the 75th anniversary of D-Day should remind us how this alliance was built, why it has survived for so long, and why it should continue.