Simplify the following text for a Grade 11 native English-speaking person.
Original: The United States Holocaust Memorial Museum says : Due to differing views and lack of documentation , estimates for the number of Serbian victims in Croatia range widely , from 25,000 to more than one million .
Simplified: Due to differing views and lack of documentation , estimates for the number of Serbian victims in Croatia range widely , from 25,000 to more than one million .