Complex sentence: After leaving the OAS Gaviria worked briefly in New York as an advisor and scholar at Columbia University, but swiftly returned to Colombia where he founded an art gallery named Nueveochenta and has remained in the country ever since.
Split into simpler sentences: After leaving the OAS, Gaviria worked briefly in New York as an advisor and scholar at Columbia University. Upon his return to Colombia he founded an art gallery named Nueveochenta, and has remained in the country ever since.