Simplify the following text for a Grade 9 native English-speaking person.
Original: In 1916 , in the wake of the Central Powers ' invasion , the valuables of the National Bank of Romania , together with many other valuables ( the Romanian Treasure ) were sent to Moscow for safekeeping , but were never returned ( except for the Pietroasele treasure - now on display at the National Museum of Romanian History , the numismatic collection of the National Bank , some paintings and archives ) .
Simplified: In 1916 , the Central Powers invaded Romania and all valuable objects of the National Bank of Romania and the Romanian Treasure were sent to Moscow for safekeeping . They were never returned .