Barak ObamaThe 28th NATO summit in Warsaw is the first of the post-Brexit era. President Barack Obama and other European leaders must address simmering problems, such as tensions with Russia that could further escalate by the expected deployment of NATO troops in Estonia, Latvia, Lithuania and Poland.

NATO members also will address the threat posed by the Islamic State and the instability caused by mass migrations; and they will talk about how to spend their money, as there is an increasing political reluctance to military expenditures.

The alliance was created in the Cold War. Despite the numerous claims of a “new Cold War” in the wake of the crisis in Ukraine, the 2016 scenario is rather different. Moscow is no longer promoting an alternative socio-economic system to compete with the West. Besides, the kleptocracy managed by Russian President Vladimir Putin cannot sustain a military machine capable of any comparison with NATO.The alliance and Obama are now dealing with the consequences of a more fragmented world and a more fragmented Europe. And there is no easy fix in the absence of a common vision.

NATO and the European Union are the two pillars that support the European continent. The two became more and more intertwined in recent years — best demonstrated by their joint mission in the Aegean Sea to stem the flow of migrants from the Middle East in cooperation with the EU Frontex agency.

“Neither NATO nor the EU are entirely equipped with the tools to tackle the unprecedented security challenges we face. But, together, we are a formidable partnership,” NATO Secretary General Jens Stoltenberg said in a recent interview.

Brexit, however, can undermine the partnership. A weaker EU risks enhancing the political divisions that emerged during the invasion of Iraq and the intervention in Libya.

Two crucial passages that highlighted the absence of a common European foreign policy.

The findings of the Chilcot report released on Wednesday after a seven-year investigation left no doubts about a truth we all knew. The British public inquiry into the UK role in the Iraq war made clear that the decision to invade Iraq was based on misleading, inaccurate and fabricated information. Former UK Prime Minister Tony Blair and President George W. Bush knew it.

In the run up to the invasion in 2003, Europe was divided in response to the U.S. plans. Germany and France, on the one hand, opposed the invasion without UN authorization and an extensive investigation on Saddam Hussein alleged weapons of mass destruction. Blair, on the other, was pushing for the invasion without further diplomatic action. The rest of Europe was busy calculating the individual advantages of backing the war plans.

We know how it ended up.

Would a stronger cohesion within Europe have made a difference? Would it have stopped the invasion? No doubts it would have helped shape a different debate. In response to the report, Blair said that “there was no middle way” and “no room for negotiation.” In fact, there was room for negotiation, but not a strong enough political actor to promote it.

The necessity of “reinventing” NATO is a popular refrain since the end of the Cold War and, recently, the presumptive Republican presidential nominee Donald Trump defined the alliance as “obsolete.”

As a matter of fact, NATO remains the most advanced military alliance on the planet, but it will be difficult for Obama, or any leader, to reinvent NATO if Europe doesn’t reinvent itself.

Roberto Capocelli is an intern in Newsday Opinion