2016 must surely rank as Nato’s annus horribilis. With Russia becoming increasingly active on Nato’s eastern borders, supporting the rebels in the Ukraine and now siding with Assad in Syria, the Nato members have been forced to refocus the alliance back towards the opponent it was originally created to tackle. As a result, defence spending is on the rise across Nato, with a target of 2 per cent of GDP applicable to all except Iceland.

They say buses come in threes, and for the Nato members three separate events, each on their own damaging enough, have called Nato’s long term survival into question in 2016.

First came Brexit. While the British government’s Brexit strategy might be unclear – as the latest leaked memo suggests – it has sought to emphasise the UK’s commitment to Europe’s defence through Nato. This has been done by committing a battalion to the defence of Estonia as part of Nato’s increased force commitments to its eastern members.

However, calls for further EU defence integration – including the creation of its own army – seem to implicitly suggest that the EU supplant Nato as the prime provider of Europe’s defence. The UK’s continuing veto on creating an EU operational headquarters can now only be a temporary delaying tactic at best and one that will be lost once Brexit goes through.

John Kerry: Turkey coup could threaten country's Nato membership

Even within Nato, the UK is under pressure and its influence in potential decline. The UK’s retention of the Deputy Supreme Allied Command Europe post is now under question, given that the post is also the designated commander of an EU force created under the Berlin Plus arrangement. With the UK’s departure from the EU, logic dictates that the post should be handed over to another EU state. France and Germany have both begun to jostle for the position.

Lurking in the shadows is a likely second referendum on Scottish independence. From a Nato perspective, the impact of Scottish independence on the UK’s defence capabilities – particularly the UK’s nuclear capabilities – is of major concern. Currently the UK remains one of only two nuclear guarantors in Nato along with the US. France, Europe’s other nuclear power, expressly excluded its nuclear forces when it returned to Nato’s integrated military structure. The prospect of the US being the sole nuclear guarantor to Europe fills many with concern, especially given Trump’s election last week.

And then there’s the failed coup in Turkey, and the resultant crackdown by President Erdogan. Turkey has a unique position within Nato: a border with Syria, control of the entrance to the Black Sea, access to the Caucasus including Georgia – and, on top of all of this, it’s Nato’s only Muslim nation. As such, Turkey remains critical for Nato’s future engagement with neighbours.

The failed coup has led to a purge of the Turkish armed forces, resulting in the Turkish air force now having more F-16 fighter aircrafts than pilots, while at the Nato headquarters only nine of Turkey’s 50 posts are currently occupied. This raises serious questions about the credibility of the Turkish military.

The surprise election of Donald Trump as US President last week throws yet another spanner into the works. At this stage, it remains unclear how much of Trump’s campaign rhetoric will bear any relation to his policies once in office. His questioning of the value of Nato to the US, and particularly the issue of burden-sharing, together with his apparent links to Russia and support for Russian involvement in Syria, have set a number of hares running.

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Already Jens Stoltenberg, the Nato Secretary General, has sought to emphasise the continuing importance of Nato as the capstone of Europe’s defence. President Obama, meanwhile, has indicated that Donald Trump will remain committed to Nato as part of his “damage control” speech-making before he stands aside in January.

For Europe, and particularly for those states that share a border with Russia and have a significant Russian minority within them, any questioning of the US guarantee to defend Europe via Article V of the Washington Treaty is of major concern, particularly if the UK’s nuclear guarantee is lost.

But even without a Trump presidency, the US “pivot” or rebalancing of its defence capabilities to the Pacific as a counter to China remains a concern. Trump is already talking of improved relations with Russia and has indicated that tackling Isis in Iraq and Syria is a greater priority. This suggests that Trump may be prepared to strike a deal whereby the US and Russia agree spheres of influence in a 21st century version of the Yalta agreement.

With Nato heading towards its 70th birthday in 2019, has its time finally run out? Four things in 2017 will determine whether we’re about to see the disappearance of the union: the results of the French and German elections (and whether there are similar Brexit/Trump effects); the result of any second referendum on Scottish independence; the effect of the continuing purges in Turkey; and, finally, what a Trump presidency actually entails.