When US President Barack Obama arrives in Cardiff, Wales, for the upcoming NATO summit, it will be at a time of turmoil for Europe. Indeed, the challenges facing the Alliance are unprecedented since the fall of the Soviet Union. After two decades of enlargement and an ongoing struggle to reorient itself after missions as far afield as Afghanistan and Libya, NATO is now faced with the specter of Russian revanchism in its near abroad.

It is a big moment for the United Kingdom, as the Wales gathering represents the first NATO meeting in the UK since the 1990 London summit – and it will be the largest single gathering of international leaders in the Kingdom’s history. In addition to leaders of NATO’s 28 member countries, including President Obama, Germany’s Chancellor Merkel, and France’s President Hollande, heads of state or senior ministers from some 60 countries will be in attendance.

Wales itself is ramping up to take advantage of the event. From a global positioning standpoint, the territory is hoping to highlight its lesser known advantages within both the UK and the EU – a strong manufacturing sector, growing commercial tech and science industries, and touristic potential.

But the summit, taking place from September 4-5, comes at something of a crossroads for NATO itself.

When US President Barack Obama arrives in Cardiff, Wales, for the upcoming NATO summit, it will be at a time of turmoil for Europe. Indeed, the challenges facing the Alliance are unprecedented since the fall of the Soviet Union. After two decades of enlargement and an ongoing struggle to reorient itself after missions as far afield as Afghanistan and Libya, NATO is now faced with the specter of Russian revanchism in its near abroad.

It is a big moment for the United Kingdom, as the Wales gathering represents the first NATO meeting in the UK since the 1990 London summit – and it will be the largest single gathering of international leaders in the Kingdom’s history. In addition to leaders of NATO’s 28 member countries, including President Obama, Germany’s Chancellor Merkel, and France’s President Hollande, heads of state or senior ministers from some 60 countries will be in attendance.

Wales itself is ramping up to take advantage of the event. From a global positioning standpoint, the territory is hoping to highlight its lesser known advantages within both the UK and the EU – a strong manufacturing sector, growing commercial tech and science industries, and touristic potential.

But the summit, taking place from September 4-5, comes at something of a crossroads for NATO itself. After a bold and successful wave of enlargement that saw the entrance of nine new members between 2004 and 2009, the push for greater European integration has largely stagnated. Qualified aspirants such as Macedonia and Georgia have been, for the past several summits, politely told that their membership is no longer a priority – and that scenario would appear to be repeating itself at Cardiff.

At the same time, the nature of NATO’s primary missions – and of the primary threats against it – are inevitably shifting.

The Alliance is in the midst of drawing down from its longest ever engagement, that of the war in Afghanistan. Meanwhile, the very fabric of the European community is under attack in the east, with the annexation of Crimea and Russia’s incremental fomenting of separatist war along the border. There are worries that NATO members like Poland and the Baltic states could be next, and the issue of how to respond to Russia’s provocations has caused splits within Europe, as well as tensions between the EU and the US.

These fears are the major reason why President Obama will make a stop in Tallinn, the capital of Estonia, on his way to the summit. While there, Obama will meet with Estonian President Toomas Hendrik Ilves, as well as Estonian Prime Minister Taavi Roivas. He will also convene all three Baltic presidents – Estonia’s Ilves, President Berzins of Latvia, and President Grybauskaite of Lithuania.

Given the trepidation in these Baltic states over Russia’s renewed disregard for international borders, Obama is expected to use this opportunity to reaffirm the transatlantic partnership – and in particular what the White House calls its “ironclad commitment” to NATO’s Article V. Article V is, in short, the cornerstone of the Alliance’s policy of collective defense against armed aggression – in the language of the founding Treaty, “the Parties agree that an armed attack against one or more of them...shall be considered an attack against them all.”

For President Obama to deliver this message in person can be seen as an amplification of recent attempts by the US to both reassure Europe’s more vulnerable states as well as to send a signal to the European powers that they must be ready and willing to mobilize on behalf of any NATO member.

In March 2014, for instance, Vice President Biden trekked to Poland and Lithuania to make the same point, and to promise additional military aid in the form of F-16 fighter jets and increased NATO air patrols over the Baltic states. And in May, Secretary of State John Kerry hosted Estonia’s Foreign Minister Urmas Paet, praising Estonia for its adherence to NATO funding goals (one of only four Alliance members to do so), and promising cooperation on diversifying the Baltic region’s energy matrix and reduce reliance on Russian gas.

For many in Washington, and in Eastern Europe and the Baltics, that reassurance is just the start. In the words of outgoing NATO Secretary General Anders Fogh Rasmussen, the Alliance must be “fitter, faster, and more flexible to address future challenges from wherever they come.”

That is why the White House is pushing for a number of proposals that would include recommitting to a 2 percent of GDP spending goal for all NATO members, expand the number and intensity of military exercises, modernize and restructure the NATO command, and update contingency planning.

Former NATO Supreme Allied Commander, Admiral James Stavridis, has argued that, in encouraging European leaders to rally around their own common defense, President Putin has gravely miscalculated. “Putin’s strategy is going to be a strategic failure,” he says. “It is instilling more resolve in the alliance and will create even more cohesion than was the case before.”

That is indeed a hopeful assessment – for no region more so than Eastern Europe. Yet without strong leadership that can overcome politically risk-averse inertia, there is still a real chance that NATO will fall victim to indecisiveness and ineffectiveness before an expanded Russian interventionism. The Cardiff summit will be a major test of NATO’s vision and resolve.