Simplify the following text for a Grade 7 native English-speaking person.
Original: Nuclear proliferation is a term now used to describe the spread of nuclear weapons , fissile material , and weapons-applicable nuclear technology and information , to nations which are not recognized as `` Nuclear Weapon States '' by the Treaty on the Nonproliferation of Nuclear Weapons , also known as the Nuclear Nonproliferation Treaty or NPT .
Simplified: When a country starts making nuclear weapons , they become a nuclear power .