Complex sentence: Jones retired from S.H.I.E.L.D. after the events of the "Nick Fury vs. S.H.I.E.L.D." six-issue miniseries (1988), but returned to help train a new corps of recruits, who were then killed by the terrorist organization HYDRA, S.H.I.E.L.D. 's primary nemesis.
Split into simpler sentences: Jones retired from S.H.I.E.L.D. after the events of the "Nick Fury vs. S.H.I.E.L.D." six-issue miniseries (1988), but returned to help train a new corps of recruits. This new class is slain by the terrorist organization HYDRA, S.H.I.E.L.D. 's primary nemesis.