Since the formation of the North Atlantic Treaty Organization (NATO) in 1949, there have been 32 summits but the most recent one held in Madrid, Spain – which brought together leaders from all the Alliance's member states - was perhaps the most important to be held since the end of the Cold War.
The Russian invasion of Ukraine in February 2022 had a dramatic effect on NATO as an alliance.
Following years of what could be termed 'benign neglect', where it was seen as a low priority by some members and an alliance struggling to define its mission by others, NATO was not in a great place.
It had struggled to define its role and work out what value it could offer in a world where it had no credible military opponent to defend against.
The invasion of Ukraine has changed this debate by re-energising and revitalising NATO as a concept and helping bring member states back together with renewed purpose to help tackle these new challenges.
The Madrid NATO summit was all about trying to work out how the Alliance moves forward and what its role is in a world where Russia has become a renewed threat.
It was a chance to review plans, confirm future goals and help reaffirm the importance of multilateral security in an increasingly complex world.
In doing so, it has committed the Alliance to a new way of working and in turn will have a major impact on how the British Armed Forces operate and equip themselves for years to come.
There are several key changes emerging from the summit that will affect how NATO seeks to defend its member states.
The most important of these is the move towards reinforcing plans to defend nations under attack – particularly the Baltic States (Estonia, Latvia and Lithuania) who share a border with Russia.
There are concerns that Russia may seek to conduct a lightning attack to link up the small enclave of Kaliningrad, captured during the Second World War from the Germans, to the rest of Russa and in doing so try to capture some of Lithuania.
Previously NATO had relied on forward deploying relatively small battlegroups into the Baltic on a non-permanent basis (e.g. they were rotated through) to help act as a deterrent to Russian activity.
The idea was that if Russia attacked, they would need to fight through small forces from lots of member states and in the process, make it far more likely that NATO would retaliate.
Under these plans, NATO do not have the ability to defend the Baltics in depth and would at best fight a delaying action in the hope of buying time while the Russians overran these nations.
Ben Wallace, the UK's Secretary of State for Defence, has admitted that it would take about 60 days to get reinforcements to the Baltic to help liberate them, by which time it would probably be too late.
Under the new plan, there will be a significant scaling up of troops and formations permanently based in Eastern Europe to help provide a more robust defence to the region.
This includes a major increase in US ground troop presence, with the US Army permanently deploying an additional brigade of about 5,000 troops to Romania and creating a Corps HQ in Poland.
This is in addition to the deployment of two additional F35 squadrons to the UK and increasing US Naval Forces in Spain.
There will now be more than 100,000 US personnel based in Europe, a significant change away from previous downward trends since 1991.
The impact of this will be to provide both a qualitative and quantitative increase in NATO forces to help deter Russia from launching an attack.
These forces will also be at an increased level of readiness compared to previous plans.
NATO now aims to have 100,000 high readiness troops able to respond to a crisis within 10 days, compared to the older target of 40,000 within 15 days.
These forces will also be pre-assigned to operate in a specific area, helping to improve contingency planning and operational exercises.
For example, the French are now assigning a Brigade to operate in Romania if required.
This marks a significant increase in readiness and will ensure the Alliance is well placed to respond to future threats from Russia.
The US is not alone in changing its plans for NATO, with other countries following suit.
Many NATO member states have now announced plans to significantly increase their defence budgets towards 2% of GDP, a key NATO spending commitment.
The result of this will be an increase in new equipment, munition stockpiles and better logistics over the next few years coming into service across the Alliance.
This spending rise will go a long way to addressing the post-Cold War 'peace dividend' that many nations applied to their budgets, putting deep cuts into their armed forces to save money.
However, it will take several years to undo these cuts and put genuinely new equipment into service.
It is also likely that some of the smaller NATO nations may struggle to spend all the money assigned to them in one go due to capacity limits in their system.
But the sheer fact they are changing means that Russia cannot take NATO disinterest for granted again – the sleeping giant that is the NATO alliance has been woken from its post-Cold War slumber.
As well as increased spending, NATO will now move more of its forces to be prepositioned and ready for operations in a much shorter timeframe.
In the Cold War, hundreds of thousands of troops stood ready to go to war at very short notice across the Inner German Border with prepositioned military equipment and stockpiles.
While it seems extremely unlikely that this will occur again, there will be an increase in ammunition, supplies and vehicles much closer to likely front lines, to improve response times in the event of a crisis.
This move, which was previously thought to be all but politically impossible, occurred just a few weeks following the Russian invasion of Ukraine.
The result is that for the first time since its founding, NATO now has a continuous land border facing onto Russia to defend well into the arctic circle and gains access to two extremely capably armed forces as allies.
Both nations have large and well-equipped modern militaries, operating advanced equipment and able to work from the outset alongside other NATO members.
This additional resource will help add significant resilience for NATO when it comes to defending the Baltic from Russian aggression.
The result is, from a military perspective, an outstanding piece of good news, which will be uniformly welcomed by other member states.
From a doctrinal perspective, the NATO Summit not only declared that Russia was the main threat facing the Alliance but also focused on the growing challenge posed by China.
While NATO may not be likely to directly confront the Chinese, the growing strength of China’s armed forces and their wider global presence means there is an increased chance of both NATO member states and China operating in the same space.
Understanding what risks China poses and what to do about this, is likely to be one of the big, longer-term questions facing NATO.
How do you balance deterring Russia, defending Europe and working out what to do with a challenge like China?
Overall, the NATO Summit has played a significant role in shaping how the Alliance will position itself to meet threats in the years ahead and should be seen as a success.
To take NATO from being relatively moribund and suffering from self-doubt around its purpose to being at the point where it has a clear vision and new members and to do so in such a short time, is a testament to how much the world has changed since the invasion of Ukraine.
All member states will now have to think carefully about how their defence plans and posture will change as a result.
For the UK, the Madrid Summit has been an opportunity to allow the Prime Minister to highlight the UK’s ongoing commitment to NATO.
The UK will significantly increase its contribution to NATO forces under the 'New Force Model' – a means of ensuring the right forces are available to support NATO operations.
This will include committing a Brigade to support Estonia as part of the pre-assigned defence planning.
More than 1,600 British troops are now based in Estonia and the presence there will be stepped up.
The UK will also contribute more troops to support operations and exercises with NATO.
For example, supporting the 'air policing' quick reaction mission with Typhoon jets, some of which are currently deployed in Romania.
More widely, the Royal Navy will make one of its two aircraft carriers available for NATO tasking, helping to improve the flexibility of NATO forces and provide an exceptionally capable ship for naval operations.
This additional ship will be able to embark not only F35 jets, but a range of NATO helicopters and could function in a troop-carrying role, enabling additional forces to carry out amphibious landings if needed.
The UK has also welcomed the expansion of the Alliance to include Finland and Sweden.
British forces have already begun increasing the number of exercises they carry out with both nations and the Royal Air Force has deployed six modern Typhoon and F35 jets to the region to build closer links with both Swedish and Finnish air forces.
It is likely there will be a similar increase in Royal Navy and British Army activity too in order to develop a strong working relationship.
The UK has long operated in the Arctic region of Norway, with the Royal Marines having a Cold War role of reinforcing and defending the area against Russian invasion.
It is likely there will be a stepping up of exercising and operations in this area, helping to ensure the UK can assist both nations as needed.
All these commitments though will come at a cost – both financial and operational.
Financially the UK is one of the few NATO nations not to have yet increased its defence budget after the invasion of Ukraine.
No additional money has been found for the MOD, unlike many other NATO partners and the British Government seems deeply unwilling to increase the capability of the armed forces beyond what has already been committed to under the 2021 Integrated Review.
This means that in the medium term, while the UK is spending at least 2% of GDP on defence, unlike other nations, it will not be adding more equipment to its military.
This has been the cause of significant political debate in London, with some politicians keen to see spending increased to reflect the new threat posed by Russia.
It seems that because of this pressure and leaked letters from the MOD to Number 10 about spending, the outgoing British Prime Minister, Boris Johnson, publicly announced that the UK would increase defence spending to 2.5% of GDP by 2030.
This commitment, seemingly rushed out with relatively little prior planning, does not seem particularly watertight, given that at least two general elections need to occur between now and then which could see the plan disrupted and never delivered on.
This leaves the MOD in a state of considerable uncertainty as it does not yet know what funding it can realistically plan on getting over the next seven to 10 years or how it can be spent.
From a planning perspective, this poses a real challenge.
Can the MOD begin to think about spending new money in the late 2020s on additional equipment that it hasn't currently budgeted for and if so, how much?
Another problem that this commitment brings will be to work out what needs to be cut if the funding doesn’t grow as expected, or new Prime Ministers or Governments take a different perspective.
MOD planners face a difficult task trying to cautiously plan for additional funds and how to spend them but doing so in a way that causes minimal impact if the funding is pulled.
This isn’t going to be an easy task to resolve.
Another issue that will be difficult to resolve is how the UK balances its commitments and interests in NATO with the wider world.
A key part of the 2021 Integrated Review was a focus on the Indo-Pacific region - the so-called 'tilt' which would see revitalised British military commitment in this area to support friends and partners.
Although not aimed directly at competing against China, it is clear the British Government wanted to play a bigger part in supporting democracies in the region.
For example, by deploying the Carrier Strike Group in 2021 to operate as part of the Five Power Defence Agreement (FPDA) exercises off Malaysia and working with Australian, American, Korean and Japanese partners to thicken bilateral military links.
The signing of the AUKUS (Australia, the United Kingdom and the United States) treaty in 2021 is another good example of this, with the UK looking to play an ever-closer role in supporting the US and Australia in enhancing regional security and cooperating on key technology issues like nuclear submarines and hypersonic missiles.
The problem is that a newly resurgent Russia will require a significant commitment to NATO to counter, including ground troops, ships and aircraft.
These can only be in one location at a time and deployments to Europe make it harder for the UK to operate in the Indo-Pacific in a meaningful way.
The risk is that as assets needed to defend Europe no longer go further East, the harder it will be for the UK to play a credible role in supporting allies in the region as it will be fully committed to NATO.
It seems likely that the UK needs to hold a new Defence Review to actively address these issues and get policy decisions on where its focus should be.
Should it focus on NATO, reassessing its equipment priorities, force levels and operational plans to be military focused predominantly on deterring, defending and (if needs be) defeating Russia?
Or should it try to strike a balance and retain a wider global perspective, but in doing so play a less key role in NATO as it will be unable to fully commit forces to the area in the same way as other partners can?
Policymakers will face some extremely difficult decisions over the next year or so, not helped by the challenge of a new Prime Minister and Cabinet keen to make their mark on national defence, as well as the possibility of a general election within the next two years as well, which could also change the shape of things politically.
While the NATO summit may have been a significant success overall for the Alliance and revitalised it at a challenging time, it also poses a significant challenge for the UK to work out how best to prioritise its defence policy, spending and plans.
It is likely that whoever ends up as the next British Prime Minister will need to lead a government prepared to make some extremely tough decisions about Britain’s place in the world and the roles its armed forces will play in shaping this.
These will be difficult to make and the outcome may be painful for many.
Only time will tell what the future holds and whether the UK intends to remain globally focused, or if the threat from Russia means it is time to focus on Europe instead.
This article is the latest contribution in our Lima Charlie columnist section.
This is part of a series featuring unattributed contributions from experts and insiders providing opinion, insight and analysis on today’s Armed Forces, the wider politics of the military and observations on military life.
Under the pseudonym Lima Charlie, our contributors aim to explore the issues facing today’s military and their comment remains unattributed to allow our writers to present their analysis candidly and under one editorial voice.