Complex sentence: The Korean royal family at the time was under siege, exiled to Ganghwa Island while Mongols took control of the mainland; the act of carving the woodblocks was considered to be a way of bringing about a change in fortune.
Split into simpler sentences: The Korean royal family at the time was under siege, exiled to Ganghwa Island while the mainland was under the control of the Mongols. The act of carving the woodblocks was considered to be a way of bringing about a change in fortune.