Complex sentence: After Choi won two championship titles in a row, he turned his attention to international competitions by participating in the IMSA Star Mazda Championship (Pro Mazda Championship) Laguna Seca Race with JDC Motorsports.
Split into simpler sentences: After Choi won two championship titles in a row, he turned his attention to international competitions. He participated in IMSA Star Mazda Championship (Pro Mazda Championship) at Laguna Seca Race with JDC Motorsports.