South Korean President Park Geun-hye warned this week that if North Korea conducts another nuclear test, it could prompt the volatile country’s neighbors to seek their own nuclear defense. “North Korea would effectively be crossing the Rubicon,” she told the Wall Street Journal.  North Korea’s last nuclear test, which took place in 2013, prompted increased Western sanctions against the country and escalating tensions between Pyongyang and its rivals. At the height of the tensions, North Korea temporarily shuttered an industrial complex that it operates jointly with South Korea, harming its own economy in the process, and offered repeated invectives against Seoul and Washington. Now, however, Western officials fear that the next round of tests could prove more threatening to the North’s neighbors. More