Even if your waking life concerns don't include nuclear holocaust, we have to admit that such an event has been at least in the back of our minds since the invention of the bomb. Take a look at all the apocalyptic-theme Hollywood movies. The film industry reflects the general mindset of society. Everyone has a fear of a nuclear holocaust.
HOWEVER, with that said, when a person does dream of some type of end-of-the-world event, it can symbolize some waking life stresses. Is there a part of you or your life that you fear could be "ending?" A relationship? A career?
Because the feeling in your dream was of fear, it seems to reflect waking life stresses. You saw overhead planes that could have been on the defense or the attack. Everyone was preparing which is a good sign as you also are preparing for any coming changes in your life.
Unfortunately, everyone in your dream felt that death was imminent. They braced for a painful impact.
Well, life changes can be painful. But the good news is that there's always a rebirth and a rebuilding after a catastrophe. Even for people to make positive changes, they need to experience a "death" of the old habits, "death" of the old ways and personalities, before the new emerges.
Is there something going on in your waking life that can be described this way?