The North Atlantic Treaty Organization (Nato) is marking its 70th birthday this week in London, but celebrations seem to be the last thing on the minds of members as the alliance struggles to get a grip on a raft of complex challenges, both internal and external.

Since 1949 Nato has acted as a bulwark against military threats to western Europe, the US and Canada and the two-day meet, starting on Tuesday, in the British capital is an opportune moment to reiterate its core principles.

While addressing Nato foreign ministers in Brussels on 27 November, Secretary General Jens Stoltenberg said: "We all agree that Nato remains indispensable for our security, and that despite our differences, we are stronger as we face the future together."

Stoltenberg's assertions might fail to convince many who see Nato's problems only mounting. 

Russia

One of the main questions facing the 29-member military alliance is how to redefine its relations with Russia. 

Cooperation stands suspended since 2014 in response to Moscow's military intervention in Ukraine, but political and military channels of communication remain open.

Nato has, however, reiterated that the alliance seeks to improve ties with Russia.

French President Emmanuel Macron went a step further, saying that Nato should focus more on terrorist threats rather than Russia.

At a joint press conference with Stoltenberg in Paris, last week, Macron said: "Our common enemy today in Nato is terrorism, which has hit each of our countries."

Defense spending

The ongoing discord over Nato's budget has escaped the attention of few. US President Donald Trump's criticism of America's allies on how they spend less on the military alliance is well-documented. 

In a bid to mollify Trump, Stoltenberg promised a hike of 4.6 percent in defense spending from European countries and Canada in 2019. He stressed they would have spent a combined $130 billion between 2016 and the end of next year.

It remains to be seen if the US president would be satisfied, or use the gathering to berate allies, especially Germany. 

Trump has urged member-states to keep to their pledge of increasing contributions by two percent of gross domestic product by 2024.

A house far from order

Perhaps, the most worrying issue afflicting NATO, presently, is a widening gulf between its members. 

Turkey's new found friendship with Russia and Ankara's military operations in Syria against Kurdish rebels have brought differences to the fore like never before.

Turkey's decision to induct the S-400 missile defense system from Moscow has raised eyebrows in Washington. In response, the US removed Ankara from its F-35 fighter jet programme.

The war of words went up a notch last month when French President Emmanuel Macron, in a controversial remark, called the coalition 'brain dead', triggering much consternation among member-states.

Macron made the "brain dead" comment during an interview with The Economist magazine. 

The 41-year-old had also appeared to cast doubt on the Nato principle that an attack on a member would be deemed as an attack on the rest, an understanding that has been the bedrock of transatlantic ties since the alliance was established. 

The future

As NATO returns to London, its inaugural home, there would be no dearth of topics to talk about. Will it result in any concerted effort to make the alliance stand on a stronger footing in a multi-polar world? That is the larger question which needs to be addressed.