A big plan between USA and Russia is over. It is called New START. This plan helped keep many big bombs safe. USA and Russia worked together for years.
Russia says it will not do the plan rules. They say USA did not agree to a new idea. This idea was to make the plan stay longer. This news makes the world not safe.
The New START plan began in 2011. It said each country can have 1,550 bombs. Countries can also look at each other's bombs. This helped make friends.
Now, the plan is over. This is not good. It means big bombs are not safe.
Russia stopped its part before. Now they say USA does not follow the plan. They say USA did not hear their ideas.
This is a bad time for the plan to end. The world has many problems. People worry about more bombs. The United Nations is sad. They want USA and Russia to talk. The world is more unsure now.