Simplify the following text for a Grade 15 native English-speaking person.
Original: After the occupation of Bohemia and Moravia on March 15 , 1939 and the Slovak declaration of an independent state , Ruthenia declared its independence ( Republic of Carpatho-Ukraine ) but it was immediately occupied and later annexed by Hungary .
Simplified: After the occupation of Bohemia and Moravia on 15 March 1939 and the Slovak declaration of an independent state , Ruthenia declared its independence ( Republic of Carpatho-Ukraine ) , but was immediately occupied and later annexed by Hungary .