Simplify the following text for a Grade 11 native English-speaking person.
Original: In 1902 the parts of the colony not organized into military districts became Senegambia and Niger , then Upper Senegal and Niger in 1904 , then the old name came back in a reorganization of 1920 .
Simplified: In 1902 the parts of the colony which were not organised into military districts became Senegambia and Niger , then the name changed to Upper Senegal and Niger in 1904 .