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In his State of the Union address, U.S. President Barack Obama described North Korea's recent nuclear test as a provocation that required a firm response. The intended audience for that provocation, though, is up for debate. Some commentators have posited that the test was a signal aimed at China, designed to demonstrate North Korea's independence from its great-power patron. Others think that Kim Jong-un was sending a message to the newly elected president of South Korea, Park Geun-hye. Still other North Korea experts have suggested that the test was actually meant for domestic consumption, to lift the sagging morale of a deprived public or for the regime to curry favor with the military. The intended North Korean signal is being analyzed and debated by U.S. government officials, who...