Complex sentence: Thebes, Athens, and Argos each provided about one quarter of the allied hoplites: 6,000 hoplites from Athens, about 7,000 from Argos, 5,000 from the Boeotians, 3,000 from Corinth, and 3,000 from Euboea.
Split into simpler sentences: Thebes, Athens, and Argos each provided about one quarter of the troops. Specifically, 6,000 hoplites from Athens, about 7,000 from Argos, 5,000 from the Boeotians, 3,000 from Corinth, and 3,000 from Euboea.