Simplify the following text for a Grade 7 native English-speaking person.
Original: The league adopted the name National Basketball Association ( NBA ) in 1949 after merging with the rival National Basketball League ( NBL ) .
Simplified: Among them , the most famous basketball league is U.S.A. league that is called N.B.A. ( National Basketball Association ) . This league was founded on August 3 , 1949 , by combination of BAA and NBL .