The U.S. government says it will stop making new, nuclear weapons, and it's reconsidering what to do with the weapons that already exist. The announcement came yesterday, two days before President Obama is scheduled to sign a treaty with Russia that would reduce how many nuclear weapons both countries have. It also comes one week before he hosts a global meeting on nuclear security. More than 40 countries are expected to attend that. But back to yesterday's announcement. This new policy would stop production of nuclear weapons. It would also invest about $5 billion in extending the life of weapons that already exist. Seven countries are officially recognized as nuclear powers, meaning they have nuclear weapons. But there are other countries that are suspected of trying to make them. U.S. officials hope this change from America will encourage other countries - all countries - to help control the spread of nuclear weapons. U.S. has promised not to use its own nukes against anyone who does that. But as Defense Secretary Robert Gates pointed out, that doesn't mean retaliation is out of the question in every situation.