Ukraine, the Middle East and Afghanistan test alliance’s future, writes Nicholas Burns

When allied leaders meet in Wales at the end of this week, they will confront three critical tests for Nato’s future.

Given all that has happened in the past half-year alone, these three challenges – Vladimir Putin’s aggression in Ukraine, the disastrous unravelling of the Middle East and an Afghanistan in peril – may make this among the most consequential summits in Nato’s 65-year history. How can it be anything less, when Barack Obama, David Cameron, Angela Merkel and their colleagues address the most immediate of these tests – how to deter the Russian president from further mayhem in Ukraine? He has instigated the most dangerous European crisis since the cold war’s end. But he has also unwittingly given Nato the impetus to restore its central role as defender of the west’s security and values.

Mr Putin raised the stakes last week with his most audacious move to date on the Ukraine chessboard. By moving Russian forces over the border to encircle the Ukrainian military, he turned the tide of battle in favour of pro-Moscow separatists. Russia’s president has effectively drawn new dividing lines in Ukraine, as well as Europe, threatening the democratic peace that had been the signal strategic benefit of the collapse of communism.

Allied leaders in Wales must counter by adopting the only measures that might give Mr Putin pause – the strongest sanctions to date, targeted on Russia’s critical financial sector. This will require the kind of unyielding political will not exhibited by Europe, especially, since the start of the Crimea crisis.Nato can also up the ante by providing sophisticated weapons and intelligence support to help Kiev take back control of the eastern part of the country. Sustained economic support for Ukraine’s sick and flagging economy is also necessary.

Ever since Mr. Putin annexed Crimea, the west has been a step or more behind him. That has to change at Newport, lest Mr Putin conclude Nato’s promises are paper thin, especially in its east where the newest allies, Estonia, Latvia, Lithuania and Poland, are vulnerable to Russian pressure.

Nato leaders understand all this. They hope to announce an expanded air and ground presence in the Baltics and pre-positioning of equipment for emergencies. They will reaffirm NATO’s Article 5 defence commitment for allies threatened by aggressors. They also want members to commit to the Nato requirement of 2 per cent defence spending (as a percentage of gross domestic product) in 10 years. All this will strengthen the Nato core. However, only tougher sanctions against Moscow will give Petro Poroshenko, Ukraine’s president, the support he needs most.

How to respond to an imploding Middle East is a second test for Nato in Wales. Europe should volunteer air support to help the US contain a rampaging Isis in Iraq and Syria. Germany, Britain and France could assist Mr Obama in persuading Sunni Arab states to squeeze Isis politically and dry up funding from wealthy Arabs. And Mr Obama will need to convince a prickly Recep Tayyip Erdogan, president of Turkey, to close his border to the export of Isis-controlled oil.

Nato leaders need to discuss how to help stabilise the disintegrating states of Syria and Libya. They should also end sordid ransom payments by many European countries to Isis and other terrorist organisations. The New York Times has reported that Europeans have paid more than $125m in ransoms to Middle East terrorist groups in the past five years in exchange for hostages – effectively helping to bankroll their operations.Nato’s military mission in Afghanistan is a third challenge. Nato is scheduled to withdraw all combat forces by 2016. But is that wise when the Taliban will inevitably mount a major offensive against a weak Afghan government? With the lessons of a divided Iraq clearly in mind, does it make sense for Nato to leave when that may imperil the Afghan unity so painfully nurtured by Nato since 9/11?

This summit is, in many ways, a generational leadership test for those assembled in Wales. This is, after all, the Nato of Adenauer, Churchill, Eisenhower and de Gaulle as well as Kohl, Thatcher and Reagan. Nato’s modern fortunes depend, in particular, on the steadfastness of Ms Merkel and Mr Obama.

The German chancellor has been the most effective conduit to the mercurial Mr Putin on Ukraine. She now needs to shift gears to convince fellow Europeans to adopt a decisive new sanctions campaign against him. Mr Obama, preternaturally calm and often diffident as a global leader, would be well advised to adopt a more vigorous leadership role.

American leaders do best at Nato when they listen to their allies, to be sure, but also demonstrate the grit and conviction necessary for allied success at times of testing. This is one of those times. A more resolute US president needs to claim Nato’s centre stage this week to guide the alliance through the multiple hazards before it in Wales.