And the rhetoric on both sides. Could the region, and the wider world, find itself plunged into war almost by accident . In south korea, the us air force is practising for war with the north. President trump is now threatening to erase north korea from the map. We will have no choice but to totally destroy north korea. Kimjong un is responding with ever bigger and more powerful missiles and nuclear tests. The us is moving ships and aircraft to the Korean Peninsula in ever greater shows of military might. Are we now on the road to war or is President Trump in danger of starting a war he doesnt want . This could go bad very very quickly. And it could go very bad very, very quickly. 0k, weve just been told to put our goggles on. The plane is descending fast. I think thats the signal we are about to go on board. This is the scary bit. Ok, thats the signal. And were down. Off the coast of south korea, three giant american super carriers are sailing together. This is an extremely rare sight. Theyve been ordered here by President Trump in the biggest show of naval might in this region for over a decade. The last time anything like this was seen in the western pacific was ten years ago. Here of the Korean Peninsula no one can really remember. This is a raw expression of americas military muscle. And for President Trump it is a message being sent to pyongyang that if it doesnt come to the negotiating table this is potentially what it faces. On board these ships are more than 200 combat aircraft. So what does it mean to have three carriers out here together . Well, the significance of our combat power as an american super carrier is our striking arm of ourcarrierairwing. And we can sustain 2a hour operations for extended periods of time. However, with more than one carrier, that length of time goes out indefinitely, quite frankly, when we get to three. In other words, if called upon to do so, there is enough firepower out here to go to war, and to keep fighting day and night. This is President Trumps responds to what has been a year of dramatic advances by north korea. On the 28th of august, just after dawn, a long range Ballistic Missile is launched from the runway of pyongyangs international airport. Kim jong un is there watching as the missile heads for space. It is the fifth missile test of 2017, but this one is different. Five minutes later and 1500 kilometres away in northern japan, air raid sirens start blaring. This is not a drill. The north Korean Missile is passing right overhead. The loudspeakers order people to find shelter. It is the first time this has happened since world war ii. For months, up and down this coast, they have been practising for this. Now, theyre doing it for real. For a japanese generation brought up in peace and security, its a big shock. Translation i want to protect my kids, but we dont have a basement, we have nowhere to hide. That missile takes only ten minutes to reach japan, what can we do in ten minutes . Translation the sirens just scare people. Theres nothing we can do. So what is the point . The government needs to have a real policy. Five days later, kim shocks the world again. Deep under a mountain near the chinese border, north korea has set off a nuclear device. Pictures show the north korean dictator looking at a new peanut shaped bomb. The explosion is huge. 20 times bigger than the bomb dropped on hiroshima. At the Un General Assembly in new york, President Trump makes his response. Rocket man is on a Suicide Mission for himself. And for his regime. The United States is ready, willing and able. But hopefully this will not be necessary. The United States has great strength and patience. But if it is forced to defend itself or its allies, we will have no choice but to totally destroy north korea. Speaking to the bbc, republican senator Lindsay Graham says this is no idle threat. I am 100 certain that kimjong un continues to develop missile technology, that can hit america, if diplomacy fails to stop him, there will be an attack by the United States against his weapon systems. Let me tell you how the war ends, it ends with his utter destruction. Before we get to that point, it might be worth trying to understand why kim jong un seems so determined to face down america with Nuclear Weapons. On december 17, 2011, north koreas long reigning dictator, kim jong il, suddenly dies. His 30 year old son is thrust into the leadership with virtually no experience. As he escorts his fathers coffin, kim jong un is surrounded by powerful old men. Walking behind him, the most powerful of all, his uncle, jang song thaek. Today, all of these old men are either dead or in prison. In 2014, kim has his uncle hauled out of a Party Meeting accused of treason and executed by firing squad. Kim jong un is systematically eliminating all threats to his power. At Kuala Lumpur International airport, a rotund north korean man is heading for check in. Moments later, cctv cameras catch the moment he is attacked by two young women, who wipe liquid on his face. Almost immediately he starts to feel ill and seeks help. Minutes later, hes unconscious, soon he will be dead. The man is kimjong nam. Kim jong uns older brother. Just a few metres away in this cafe, at one of those tables, four north korean men were sitting watching. All four are now wanted by malaysian authorities. One is reported to be a known north korean security agent. After the attack here was over they got up and headed for departures. Kim jong nam has been poisoned with vx, a rare and deadly nerve agent. Almost certainly supplied by the agents sent by his younger brother. Why would kim jong un want his older brother dead . In the south korean capital, seoul, ive come to meet a man who once served in kim jong uns palace guard. He describes the regime obsessed with security and paranoid about being overthrown. Translation to the kim family everyone is a potential enemy. The north korean military, the general staff, the entire north korean population. Anyone who opposes kim is an enemy. Even blood relatives. This man says kims Nuclear Quest is likewise about survival. And that it intensified after the overthrow of libyan dictator colonel gaddafi in 2011. The reason why the kim family is obsessed with developing Nuclear Weapons is to protect and maintain the regime. If the us attacks the north, it will use everything to strike back. But kim will not risk losing the regime by attacking first. Kim jong un is not stupid. Nuclear weapons serve another purpose. To secure kims own power and legitimacy. In every recent test he has been there, personally supervising, cigarette in hand. President trump calls him little rocket man. But to his own people kim is now the leader who has ta ken their country into a very exclusive club. It is no small feat. The question now is can anything be done to stop him short of war, that everyone says they do not want. For us, in a way, the most important thing is not whether hes homicidal, its whether hes suicidal. Because whether we go to war or not, it might well depend upon whether we think deterrence works, or whether we need a preventive war. Because we cant fall back to deterrence. If hes not suicidal, hisjust homicidal, then im prepared to argue lets rely on deterrence. At gunsan airbase in south korea, the United States air force is practising for war with the north. Im getting a very rare opportunity to see what that means. Flying in the back seat of an f 16 fighter. Up front is colonel steve tittel, callsign wolf ii. Were heading out on what they call here a red flag. Simulated air to air combat. Were going to go ahead and were going to engage them. 0k. Ourjob will be to play a north korean intruder. Up ahead, two blue team f 16s are waiting to stop us. Were going to engage the one on the right side. Passing right over the top of us. Which, as an adversary, is exactly what i was hoping would happen. Wolf ii makes repeated high g turns as he tries to get a missile lock on the defending aircraft. In the back, it feels like an elephant is sitting on my chest. To stay in the air and keep fighting, thesejets need to be refuelled once every hour and a half. This is not a game, there is a very serious point. This is deterrence at work. Wolf two and his fellow pilots practice every day so that north korea knows if it ever attacked the south it would be attacking the United States, too. I want to be ready because i want to send the message of deterrence, and the message of, leave us alone, you dont want to mess with us. But if you make the mistake of straying across touchline, may god have mercy on the wolf packs prey, because we are ready. Readiness is our currency and we have money in the bank. For over 60 years, this strategy of being ready to fight tonight has kept the peace. But north korea has never had the ability to directly strike the United States. Until now. On november 28, north korea again shocks the world. In the middle of the night it launches a new missile. This one is huge. Much more powerful than anything pyongyang has launched before. Large enough to carry a Nuclear Warhead all the way to washington, dc. Two hours later, President Donald Trump tries to sound calm as he absorbs the news. Thank you very much. As you probably have heard, and some of you have reported, a missile was launched a little while ago from north korea. I will only tell you that we will take care of it. We have general matters in the room with us and weve had a long discussion on it. It is a situation that we will handle. In the days that follow, americas most advanced Stealth Fighter jets start landing at bases in south korea. It is now perhaps only months before north korea will be able to hit america with a reliable nuclear tipped missile. Former state Department Officials like david straub say this fundamentally changes the equation. Whether we will be content to continue just containing north korea as weve done when they can actually hit us is the big question. And its a very difficult question. Because there is no way that American News can know for sure whether north korea will never use those weapons against the United States. Even if we dont provoke them in any way that we regard as provocative, we cant be absolutely sure they wont someday attack us. What would it mean for america to go to war . In south korea, i am on the road to the demilitarised zone. The four kilometre wide strip of land that separate south korea from the north. This is the most heavily fortified place on earth. The south has hundreds of artillery pieces pointing north. The north has thousands pointing back. This recent north korean propaganda video shows its massed artillery in action. For South Koreans living close to the demilitarised zone, this makes for very uncomfortable viewing. The little town of hwacheon is just six kilometres from the dividing line. In any new conflict, people here would have only minutes to evacuate. This place was built about five years ago. Underneath a mountain. And it is absolutely vast. Its 100 metres long, 20 metres wide, and so big its got its own echo. Listen to this. Hello the shelter is designed to take over 2000 people. If they can make it in time. This 86 year old woman is one of the few still living here who remembers the last korean war. Are you worried there could be war again now . Translation of course im worried, but what can i do . Its up to the government. And leave, then ill leave. If they saying i should die, ill die. A much bigger target for north koreas artillery is the south korean capital, seoul. Half the south korean population lives in the greater seoul area. 25 Million People. Andrei lankov is a long time seoul resident and professor of north korean studies. So 25 Million People is within the shooting range of the north korean artillery, which is located that direction, roughly, say, 20, 30 kilometres from here. And if we have a conflict, the city will be attacked by the conventional weapons which will lead to thousands of casualties in the first few minutes. Many more in the first few hours. If it happens, most likely the South Koreans will strike back and there is a second korean war. A second korean war would be bad enough. But this time it could go nuclear. That thought brings horror to the people of this place. Hiroshima. When that happens for you here. Keiko still remembers vividly the sunny morning of the 6th of august 19115. She was eight years old. Yes, every time i come here, you know, by the river, i remember it quite well. So many people died in the river. Those like keiko, who survived the worlds first atomic attack, are worried the world has forgotten the true horror of nuclear war. We have to avoid, stop, america will use their power to attack north korea, because not only Korean People north and south, and the chinese, we japanese, everybody will be involved. Even though they dont use Nuclear Weapons. But they will have a very big casualty. This year, kim jong un has repeatedly shocked the world, taking giant leaps towards his goal of a full nuclear arsenal. He is now threatening to carry out an Atmospheric Nuclear test over the pacific ocean. If he did, President Trump might feel he has no option but to order a military strike. The president is following his instinct. And his instinct, if hes challenged, as he has been by the north koreans, is, as he says sometimes, hes a counterpuncher, to punch back. This could go bad very, very quickly. And it could go very bad very, very quickly. And a lot of people can die very, very quickly. Winston churchill once said that meeting jaw to jaw is better than war. But pyongyang says it will not talk to america until it accepts north korea is a legitimate nuclear state. Washington is adamant that will never happen. And with each new test, the pressure on the american president to act grows stronger. It is going to be quite chilly first thing on saturday, certainly with a good frost around. But the weather will turn milder over the next few days. By the time we get to sunday, i suspect double figure temperatures across of the uk. At the moment there is a dip in the jetstream which brings in cold air from the north. Here, we start to see a south westerly flow of air, which will push the weather front and cloud in our direction and this area of milder air will be in place across the uk by the time we get to sunday. But saturday is still going to be quite a cold day across most of the uk. The cold snap is still not quite over. Look at this. Were still getting weather watcher pictures with nice, snowy scenes across the uk, mostly across the hills now. First thing on saturday morning, a widespread frost across the country. These are the city temperatures. In rural areas it will be much colder. Saturday morning start off on a beautiful, crisp note, through plymouth and bournemouth, all the way to brighton and dover. The midlands also nice and crisp temperatures around. 1 in nottingham. Freezing across most of the yorkshire. Into scotland as well. We start to see slightly milder air at this stage getting into parts of northern ireland. On the whole, a nice start to the day, but there will be a change on the way later on on saturday. Clouds will be increasing and it might turn cloudy across wales and maybe around merseyside, into the West Midlands and the south west here. At times it could rain everywhere on saturday. The best of the sunshine in the east and the south east and the far southern counties. Then the change happens to be mild weather through the course of saturday night into sunday. The weather front comes off the atlantic and we develop a south westerly wind. So that milder air will arrive through the early hours of sunday and for many of us sunday will be at least starting off on a cloudy, damp note. Quite breezy too for a time. We could even see Gale Force Winds across the far north. Temperatures back up to double figures, even in scotland. That damp weather will last right through the course of sunday but by the time we get to monday it looks like things will be drying out. A little bit of a dip in the temperature. Into next week, it looks like the weather will dry out but its still going to stay relatively on the mild side. Hello and welcome to bbc news, im gavin grey. Eu leaders have confirmed that brexit negotiations can move on to the next stage, but they have warned the talks will be even harder. Theresa may called it an important step on the road to a smooth and orderly brexit. Here is laura kuenssberg. The men with the message part one is done. The European Union is ready to grant the prime ministers wish and move on. She was a tough, smart, polite and friendly negotiator. And so we were able to conclude that sufficient progress has been made