Complex sentence: It featured two Shields, Joe Higgins, who led the series for the first thirteen issues before being replaced with Lt. Michael Barnes who continued as The Shield up until the title ended in October 1992.
Split into simpler sentences: It featured two Shields, Joe Higgins, who led the series for the first thirteen issues, and Lt. Michael Barnes, his replacement. Barnes continued as The Shield until the title ended in October 1992.