Simplify the following text for a Grade 11 native English-speaking person.
Original: Together they returned to the Amazon in 1948 , and after that expedition he penned `` Where Civilization Ends '' ( Donde La Civilizacion Termina ) .
Simplified: Together they returned to the Amazon in 1948 , after which he penned `` Where Civilization Ends '' ( Donde La Civilizacion Termina ) .