Complex sentence: These methods, identified only as "Native Sword Methods" (K. "BON KUK GEUM BEOP-본국검법") had been been brought to China during a time when Chinese sword work had declined and were ascribed to about the 9th Century by Mao.
Split into simpler sentences: These methods, identified only as "Native Sword Methods" (K. "BON KUK GEUM BEOP-본국검법"). Mao reports that these methods had been been brought to China during a time when Chinese sword work had declined and were ascribed to about the 9th Century by Mao.