Complex sentence: While the gum industry prospered, the Cubs grew less competitive over the decades, with a brief flurry of success (although no championship) in the late 1960s and early 1970s.
Split into simpler sentences: While the gum industry prospered, the Cubs grew less competitive over the decades. They did have a brief flurry of success (although no championship) in the late 1960s and early 1970s.