Complex sentence: The "death" of the liberal class follows from this dearth of new ideas, because the "liberal class" is cut-off from the sustained energy and life that new ideas provide.
Split into simpler sentences: The "death" of the liberal class naturally follows from, and is the direct consequence, of this dearth of new ideas. Now the situation is such that the "liberal class" is cut-off from the sustained energy and life-blood that new ideas provide.