Complex sentence: Although they were outnumbered in the area by a factor of roughly 10:1, the Japanese waged a dogged resistance campaign, which continued until the end of the war, by which time most of the original defenders, and more than 100 Australians had been killed.
Split into simpler sentences: Although they were outnumbered in the area by a factor of roughly 10:1, the Japanese waged a dogged resistance campaign. Nevertheless, fighting continued until the end of the war, by which time most of the original defenders, and more than 100 Australians had been killed.