
Those first bombs were very strong, but the nuclear bombs we have today are much, much stronger. A single modern bomb dropped on a big city like London could kill more than one million people instantly.
Today, nine countries have these nuclear weapons. The United States and Russia have the most, with about 4,000 bombs each. That is enough to destroy the world. Other countries are also building more bombs.
This is a very dangerous situation. The world feels more unsafe now because countries are not agreeing on how to control these weapons. The scientists who first imagined the bomb hoped it would only be used to prevent war, not to start one. People hope these terrible weapons are never used again.
