Complex sentence: As the Soviet economy was stagnating, Gromyko's diplomatic skills were of less importance as, during the leadership of Yuri Andropov and Konstantin Chernenko, Gromyko had adopted a more hard-line position than his superiors.
Split into simpler sentences: As the Soviet economy was stagnating, Gromyko's diplomatic skills were of less importance. During the leadership of Yuri Andropov and Konstantin Chernenko Gromyko had adopted a more hard-line position than his superiors.