Complex sentence: By the time of the Peloponnesian War the democracy in Athens was around 100 years old, most of the upper class accepted this form of government either vying for positions of leadership within it or remaining aloof outside of it.
Split into simpler sentences: By the time of the Peloponnesian War, the democracy in Athens was around 100 years old. Most of the upper class accepted this form of government, while either vying for positions of leadership within it, or remaining aloof outside of it.