Complex sentence: Construction on the new stadium began in 1977 with the aim of staging the Asian Games in 1986.When Seoul was awarded the Games of the XXIV Olympiad in September 1981, this stadium became the centrepiece.
Split into simpler sentences: Construction on the new stadium began in 1977 with the aim of staging the Asian Games in 1986. However, when Seoul was awarded the Games of the XXIV Olympiad in September 1981, this stadium became the centrepiece.