Simplify the following text for a Grade 5 native English-speaking person.
Original: Nauru is the world 's smallest island nation , covering just 21 k. Settled by Micronesian and Polynesian people , Nauru was annexed and claimed as a colony by the German Empire in the late 19th century . After World War I , Nauru became a League of Nations mandate administered by Australia , New Zealand , and the United Kingdom .
Simplified: Nauru is the smallest republic in the world .