Simplify the following text for a Grade 9 native English-speaking person.
Original: Established on April 7 , 1948 , with headquarters in Geneva , Switzerland , the agency inherited the mandate and resources of its predecessor , the Health Organization , which was an agency of the League of Nations .
Simplified: The World Health Organization ( WHO ) is part of the United Nations ( UN ) , working on international public health , with headquarters in Geneva , Switzerland . The WHO was established by the UN on April 7 , 1948 .