When the war comes and the city is bombed, Montag has a horrible vision of Mildred still standing in her TV parlor, living with her "family" without knowledge or care for her impending death.
He saw her in her hotel room somewhere now in the half-second remaining with the bombs a yard, a foot, an inch from her building. He saw her leaning toward the great shimmering walls of colour and motion where the family talked and talked and talked to her, where the family prattled and chatted and said her name and smiled at herand said nothing of the bomb...
(Bradbury, Fahrenheit 451, Google Books)
This reaction, it is implied, is repeated by people all over the city, people who are so obsessed with their meaningless entertainment that they have paid no attention to the growing concern of war. News and politics are of less interest to them than their own instant gratification, and so they are not worried about the bombs. After all, if it doesn't happen on the television screens, it isn't real. Some people leave the city, but the vast majority remain, content in their bubbles of personalized television. Without someone telling them what to think and how to process information, they had no way of realizing that the impending war was actually real and actually a threat to their own lives.
People have become numbed to idea of war. We learn that the country has won two nuclear wars since 1960 and that bombers are constantly flying overhead, so that the very idea of bombing has become normalized.
Jesus God," said Montag. "Every hour so many damn things in the sky! How in hell did those bombers get up there every single second of our lives! Why doesn't someone want to talk about it? We've started and won two atomic wars since 1960. Is it because we're having so much fun at home we've forgotten the world?
When the bombs do come, they come so quickly—a fact of modern warfare—that people hardly have time to worry. Further, most people are probably, as Montag envisions Millie, so absorbed in the fantasy world of their view screens that they don't even know what's happening. Bradbury describes a world in which people are so secure in their mindless material comforts that they have lost touch with the idea of suffering, even if they are, like Millie, desperate because they know subconsciously that they have given up their souls.