As befits most public documents issued at international gatherings, the communique released at the end of the North Atlantic Treaty Organisation’s summit in Warsaw was both long and tedious, covering every conceivable global security threat apart, perhaps, from the eventuality of Martians landing on Earth.

But notwithstanding the communique’s verbosity, the decisions taken by the 28 heads of states and governments represent a fundamental shift in the history of the US-led alliance in Europe. This is the first time NATO displayed a determination to come to terms with Europe’s post-Cold War security reality; what was decided at Warsaw over the weekend will determine Europe’s security map for many years to come.

The first and probably most fundamental shift was psychological, featuring nowhere on the pages of the final communique: the former communist countries of Central and Eastern Europe finally ceased to be second-class partners and became equal allies. NATO opened its doors to 12 of the nations which used to languish behind the Iron Curtain in three staggered phases, in 1999, 2004 and 2009. Although the new member-states were entitled to be heard, they seldom influenced NATO’s major strategic decisions.

That’s no longer true, as anyone who attended the summit can testify. The chairman of the Military Committee, the body responsible for the unified defence of the North Atlantic region, is now a four-star Czech general. Officials from the former communist nations are now prominent in many of the Alliance’s other structures. And most of the discussion in Warsaw was—with an irony not lost on anyone—about the future security arrangements of a region which used to belong to the Soviet-controlled Warsaw Pact.

In the process, another major transformation took place: NATO leaders accepted to deploy four battalions—totalling about 4,000 troops—to Poland as well as the Baltic States of Estonia, Latvia and Lithuania. The deployment itself is hardly significant in military terms and the Alliance was careful to stress that it’ll consist of soldiers being rotated from various member-state nations. But the political and strategic message which NATO conveyed is significant.

The forward deployment is designed to act as a warning to Russia that, although the Alliance did nothing to protect the territorial integrity of Ukraine against a Russian military invasion in 2014, NATO won’t flinch from activating its famed mutual security guarantee should the sovereignty of its member-states in the Baltic region be threatened. That’s why NATO has chosen some of its most powerful militaries to provide the ‘lead framework nations’ duties for these deployments: the battalions and their rotations will be led and organised by the US, Britain, Canada and Germany, all pointed reminders to Moscow that, should it chose to test these new arrangements, it won’t be dealing with minions.

The atmosphere at the summit was also more collegiate and friendly than at any time in the past decade. For once, the Central and East Europeans didn’t feel the need to plead for their security. The old, almost theological dispute on whether NATO should concentrate on protecting Europe or devote more resources to so-called ‘Out of Area’ crises around the world is also largely over. Although allies and partners—including Australia—currently contributing to NATO’s Resolute Support Mission in Afghanistan met with President Ashraf Ghani in Warsaw and agreed to continue the mission beyond this year, the reality is that the Alliance will from now on concentrate on its own continent; ‘NATO is coming home’ as one official privately put it.

Calm also reigns over budgetary disputes, once one of NATO’s most controversial topics. The US still accounts for around 70% of NATO’s assets and contributions, and continues to ask the Europeans to do more. But the Americans accept that defence spending trends are in the right direction: Britain and France are pledged to devote 2% of their GDP to their militaries, as are all the East Europeans. Even the Germans, who are still lagging behind, now accept that their military spending will have to increase.

Yet just when the Alliance seems to have regained its poise in every field, NATO faces new political trouble from one of its most stalwart members: Britain. Although the decision of the British electorate to leave the EU doesn’t formally affect British membership in NATO, it does have the potential to upset Europe’s delicate security arrangements.

Over the weekend in Warsaw NATO and the EU agreed to work together on protecting Europe’s shores from the challenge of illegal immigration, and on tackling the so-called ‘hybrid threats’ from Russia—namely the destabilisation techniques conducted by Moscow through a variety of sympathisers and organisations in the West.

But nobody knows how the British will treat these plans for cooperation once they are out of the EU. A future British government may decide to act as a hindrance to EU-NATO links, particularly if Britain gets a bad ‘divorce’ deal from the EU over trade and other economic matters. Or London may end up acting as a bridge between the two institutions, offering a good service to both. Speculation was rife in Warsaw on this matter but no conclusion could be reached, since there were as many opinions as there were delegates.

One issue united all, however; affection for Barack Obama, who attended his last NATO summit. The US President never quite warmed to NATO; he didn’t cherish being surrounded at summits by all those generals in national uniforms and made no secret of his opinion that America’s key security challenges stem from Asia, rather than Europe. Still, he concludes his presidency by pledging more US cash and troops to NATO, and by calling for NATO’s ‘reinvigoration’.

Altogether, not a bad outcome for an organisation which is one of history’s longest-lived military alliances, and remains the wold’s most powerful military bloc.