Original sentence: Sparta had now built a fleet (with the financial help of the Persians) to challenge Athenian naval supremacy, and had found a new military leader in Lysander, who attacked Abydos and seized the strategic initiative by occupying the Hellespont, the source of Athens' grain imports
Edited sentence: Sparta had now built a fleet (with the financial help of the Persians) to challenge Athenian naval supremacy, and had found a brilliant military leader in Lysander, who attacked Abydos and seized the strategic initiative by occupying the Hellespont, the source of Athens' grain imports