The USA is worried about hypersonic missiles. These can travel 20 times the speed of sound. They are a security problem for the USA. It could not stop Russia or China using these missiles, so it needs its nuclear weapons. U.S. President Donald Trump will meet Russian President Vladimir Putin soon to talk about the arms race.
Russia tested a hypersonic missile this month. President Putin said Russia needs the weapons because "unlawful sanctions" hurt Russia's development. He said: "You have failed to contain Russia." Mr Putin says the missiles can "strike like a fireball". The poisoning of a Russian spy in England this month has made relations worse.