Complex sentence: As the Japanese advance continued, the Australians withdrew back to Imita Ridge, but from there the Australians subsequently launched an advance which saw them pursue the Japanese--who had reached the limits of their supply line--back to the beachheads on the northern coast.
Split into simpler sentences: As the Japanese advance continued, the Australians withdrew back to Imita Ridge. The Australians subsequently launched an advance which saw them pursue the Japanese--who had reached the limits of their supply line--back to the beachheads on the northern coast.