Dr Rob Johnson, director of the Changing Character of Conflict Centre at Oxford University, said China is taking the steps that would be expected to have the ability to attack Taiwan, while Russia could well be readying to launch military operations against a NATO country.
This comes on top of Vladimir Putin's full-scale invasion of Ukraine, which is in its fifth year, and the US and Israeli war against Iran.
Mr Johnson has compiled a list of 80 "indicators of conflict preparation and coming armed attack" by drawing on the lessons of history, including the run up to the Second World War.
The indicators cover the kind of military activity and hostile diplomacy demonstrated by a nation that is preparing to launch an armed attack, as well as societal changes and government information campaigns.
Asked how many of them are already flashing, Mr Johnson said: "If you look at the whole list, we're about 94%, 95% complete.
"In other words, we're really quite close to the threat of an armed conflict."
Countries that are planning military action typically need time to ready not just their armed forces but their industrial base, economy and population.
Mr Johnson said one early indicator of future belligerence is when a nation starts to significantly expand the size of its navy - something that can take up to 20 years.
There would also be the construction of additional infrastructure to facilitate troop movements or defensive positions.
"You might see railway lines being layered," Mr Johnson said in an interview at his office at Pembroke College. "Tunnels, bunkers, maybe depots being created. It takes time."
Then - closer to an attack - there would be increased military activity, such as training exercises, missile tests, and extra recruitment of personnel.
Diplomatic language would become more aggressive on the world stage, including withdrawing from treaties, recalling ambassadors or severing diplomatic ties.
A government would also need to take extraordinary steps domestically, perhaps by restricting movement, rationing food and fuel, and using TV, radio, and online platforms to promote patriotism and demonise outsiders.
In the final months, weeks or days, you would see the mobilisation of troops towards their intended target as happened when Russia launched its attack on Ukraine in 2022.
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"We saw mobile crematoria being deployed to the border," Mr Johnson said. "We saw, in the last 24 hours, blood banks being delivered to forward medical units. And, because blood is hard to preserve, it's the last indication. You know you've got 24 hours left. They're coming."
As well as plotting the warning signs of war, the academic also mapped out the actions that other nations might be expected to take in response.
"What we end up with is a sort of line of responsiveness," he said.
It starts with monitoring what is happening, then if suspicions grow, it moves to diplomacy and greater intelligence gathering to gain a better understanding of a country's intent.
If the indicators of war continue to flash, rival governments need to put themselves on a war footing too - either to deter any aggression or to be ready to defend themselves in a fight.
In the 1930s, as German defence spending rocketed, the UK took similar action, rapidly expanding its industrial base to be able to produce more weapons, with car factories converted into Spitfire production lines and "shadow factories" built next to existing sites.
Mr Johnson said the contrast with today could not be starker.
Even though war is already raging in the Middle East and Ukraine, he said Sir Keir Starmer has failed to respond with a significant, rapid increase in defence spending coupled with the ramping up of what is left of the UK's defence industrial capacity.
"The lack of preparation I find astonishing. Actually, no, I use the word breathtaking," the academic said.
"I would expect to see a rapid expansion of the Royal Navy, a rapid improvement in munitions production in the UK, co-production with Europe... Crucially, I also would like to see the public being informed properly about what the threat is."
Asked what his warnings and indicators timeline said about the potential threat posed by China, Mr Johnson said: "China is well along that line.
"You've got so-called wolf warrior diplomacy... We've seen the rehearsing, large-scale naval exercises… They have been building, rearming rapidly, massive defence spending…And perhaps most worrying of all, they've made a declaration they're going to have a thousand nuclear warheads by 2030."
As for Russia, even though its forces are fighting in Ukraine, they are also rearming at home.
It means, Mr Johnson said, that the warnings and indicators of a plan for a potential Russian attack against a NATO nation are also evident.
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"We're at that moment now, a bit like the winter of 1939, where our key threat actor, Russia, is now ready to attack. They're getting ready. They're at full production of munitions. And we are still hesitating, hoping that perhaps this won't happen."
Sky News is the official media partner of the London Defence Conference 2026. Later this year Sky News will launch a new defence & security app, bringing together video-first reporting from our leading journalists and experts.
But General Onno Eichelsheim told Sky News that he still believed the United States would come to the defence of a NATO nation if requested, saying the kind of interactions he has on a military level, including with his US counterpart General Dan Caine, were unchanged.
"If we ask them to help us out, they will do it," the Chief of Defence (CHOD) of the Netherlands said in an interview on the sidelines of the London Defence Conference.
The US president, who has long viewed NATO with disdain because of its over-reliance on US military strength to protect Europe, said in recent days that he is considering pulling out of the alliance, dismissing it as a "paper tiger".
He also said he is "very disappointed" in his allies after he asked for their support in his war against Iran - even though he then said he did not need it - and they stayed away.
Mr Trump even hinted this meant he would no longer be willing to help an ally in distress - undermining a founding principle of the alliance under Article 5 of the NATO treaty that an attack on one member state is an attack on all.
"Why would we be there for them if they're not there for us? They weren't there for us," he said.
Asked whether comments like that were weakening NATO and its ability to deter Vladimir Putin, General Eichelsheim said: "It never helps, because our best deterrence is having an alliance that looks as an alliance.
"But on the other hand, I must say, if I look at my own work that I do, even with Dan Cain or with the Americans, on our CHOD level and on the military level, there is no change in the behaviour of the US.
"I am fully convinced that they will comply to Article 5. If we ask them to help us out, they will do it."
At the same time, he said it was vital for European nations to step up and do more to defend themselves - something Mr Trump has repeatedly requested to ease the burden on the US.
"It is our continent, it's mostly our threat," the Dutch military chief said.
"Russia is also a threat to the Western world and to the US. But it's primarily on our own door. So we have to step up for that as well.
"So, I understand that rhetoric, if you can call it like that, of President Trump. But it is not good to use also rhetoric like, 'Well I am not sure if I will help the nations in NATO'.
"That is, I think, not a wise thing to say."
All NATO allies, under pressure from Washington to do more, agreed at a major summit in The Hague last year to increase spending on core defence to 3.5% of GDP by 2035 and to spend a further 1.5% of GDP on less-well-defined security areas.
But it will take time before European member states and Canada develop the military capabilities and capacity to take on a significant chunk more of the fighting power that the United States armed forces bring to Europe's defences.
General Eichelsheim said he thought it would be between five to 10 years until European allies are able to fulfil the kind of capabilities that the US brings.
Asked what sort of percentage of NATO military power to defend Europe would then be European, he said: "Around 60-70% and that will make sense from my perspective."
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The lag time between European militaries saying they are rearming and actually being ready, created what the general described as a "vulnerability window" between 2028 and 2030 when Russia could attack.
He said for now Mr Putin's forces were too busy fighting in Ukraine to have the capacity to open a new front against NATO. But they only needed 18 months to prepare, should a ceasefire be agreed between Kyiv and Moscow.
Asked how likely he thought it was that the Kremlin might try to exploit NATO's window of vulnerability, the Dutch commander said: "I have to prepare for the worst...
"I am not sure if he will not, somewhere in time, wake up like that, because he is not predictable. He has said too many times that he wants to challenge, so we better listen to that and prepare ourselves for that."
Sky News is the official media partner of the London Defence Conference 2026. Later this year Sky News will launch a new defence & security app, bringing together video-first reporting from our leading journalists and experts.
The youngsters were inside the blue car travelling along Gilmorton Lane towards Lutterworth when the vehicle left the road bridge at around 1.30pm on Friday, Leicestershire Police said.
Four people in the minibus, a white Fiat Ducato driving southbound on the M1, were injured in the collision with the car and taken to hospital.
Three women remain in hospital with non-life-threatening injuries, while the male driver of the minibus has been discharged.
The two teenagers in the car were declared dead at the scene.
The crash happened shortly before junction 20 and the M1 remained closed for several hours while forensic work was carried out.
Police, Leicestershire Fire and Rescue Service and East Midlands Ambulance Service attended the scene.
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Officers would like to hear from anyone who was driving on Gilmorton Lane or on the M1 in either direction near junction 20 at around 1.30pm on Friday.
Police are asking anyone with dashcam footage or who saw either vehicle to contact them.
The crash happened at 1.15pm local time on Friday when the bus plunged into a ravine on the GM-2 highway in La Gomera.
All of the passengers, 24 adults and three children, were British.
The person killed in the bus crash was a British man, the Foreign Office has said. He was aged 77, it is understood.
Four people are seriously injured, emergency services in the Canary Islands said in an update.
"Emergency health services attended to the 28 occupants of the bus, 27 tourists of British nationality and the driver," local officials said.
Foreign secretary Yvette Cooper said in a post on X: "My thoughts are with those affected by the tragic incident involving a bus carrying British holidaymakers in the Canary Islands."
She said the government was in touch with the local authorities and ready to support the Britons and their families.
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Two of the most seriously injured, a 73-year-old man and a 42-year-old man, were airlifted to hospitals on the larger neighbouring Canary Island of Tenerife.
Two people with serious injuries were being treated at Nuestra Senora de Guadalupe Hospital in San Sebastian de La Gomera on the island where the crash took place. Another 23 with minor injuries were also taken there.
Images shared by the Canary Islands government on social media appear to show the bus had come off the road at a hairpin bend.
The GM-2 road where the incident took place is high up, with spectacular views out to sea. La Gomera, the second smallest of the eight Canary Islands, is marked by the steep terrain of volcanic mountains, dense forest and cliffside villages.
A statement from the British embassy in the Spanish capital, Madrid said: "Our thoughts go out to those affected by this tragic incident.
"We are aware of the situation, and we stand ready to support British nationals.
"We are also in touch with local authorities on the ground."
A Foreign Office spokesperson said: "We are supporting the family of a British man who died in the bus accident in the Canary Islands and are in contact with the local authorities."
Air Chief Marshal Sir Richard Knighton said the updated iteration of what was called the Government War Book would require people to think differently about resilience, drawing on lessons from the Cold War but "in a modern context, with a modern society, with modern infrastructure".
In an interview on Friday at the London Defence Conference, he also revealed that a threat by the UK to seize ships that are part of Russia's murky "shadow fleet" is already having an effect, even though British forces have yet to board any vessels.
The chief of the defence staff said the mere knowledge that London was ready to target a sanctioned tanker was forcing Moscow to escort them or divert them away from UK waters.
However, shadow fleet ships have still been spotted off the coastline without being stopped.
Asked whether an actual boarding operation was imminent, Air Chief Marshal Knighton said: "Be in no doubt. We are ready."
Perhaps the biggest challenge for the military chief is a push to put the Royal Navy, army and Royal Air Force back on a war footing after decades of underfunding under previous Conservative and Labour governments since the collapse of the Soviet Union.
Sir Keir Starmer and John Healey, his defence secretary, have promised to lift defence spending to 3.5% of GDP from just over 2% - but not until 2035.
They are also yet to release a crucial 10-year investment plan for the armed forces - which sets out what weapons and capabilities the Ministry of Defence (MoD) will procure.
The Defence Investment Plan should have been published last autumn - but Mr Healey, in a separate Sky News interview, would not even say whether it would be out by this summer.
The delay means much of the UK's defence industry is in limbo, awaiting the promise of new cash to become a reality.
Air Chief Marshal Knighton signalled that the hold up was because the MoD was holding out for more money to be made available from the Treasury faster.
"What I want is a defence investment plan that is properly funded and delivers what we want," he said.
"If that takes a bit longer, I'd rather have something that works and we can deliver."
A key revelation in his comments was about the plan, led by the Cabinet Office and involving all other government departments, to produce a new version of the old war book.
Conceived during the First World War, the government's previous collection of top secret, regularly rehearsed and updated war books made the UK one of the best prepared nations in the world for conflict - and one of the most resilient.
A 1976 copy - a large bundle of hand-typed pages, bound together by string - contained detailed lists and signposted the way to complementary plans about how to mobilise not just the military but also civilians and industry in a crisis, as well as shutting schools, clearing hospitals, rationing food, and even storing national treasures.
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That all changed after the Cold War ended and by the early 2000s, the entire UK war book system, which cost a lot to maintain, was quietly shelved.
Asked whether Britain was reviving the old government war book, Air Chief Marshal Knighton said: "I think that's right."
He set out what that would look like.
"NATO describes the transition to conflict as a military component, but it also has a civilian component," the defence chief said.
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This includes ensuring critical national infrastructure, such as power stations and water supply, are resilient not just to natural disasters such as floods but also to the threat of war.
"I talked before Christmas of the need that when we think about renewing our water infrastructure or electricity or transport infrastructure, to think about the threat of action from an adversary that is above the threshold of war, not just a hybrid threat," he said.
"And think about how we build in that resilience as we renew it and that requires making some different choices and different priorities and that work that the Cabinet Office is doing across the whole of government is something that I really welcome."
He said civilians need to be aware that the relative peace the UK has enjoyed over the past 30 years is under increasing threat.
"That requires us to educate ourselves and help the population understand some of those threats and help them understand what they can do to support the nation and potentially support the armed forces."
Sky News is the official media partner of the London Defence Conference 2026. Later this year Sky News will launch a new defence & security app, bringing together video-first reporting from our leading journalists and experts.