North Korea's ruling Workers' Party has again chosen Kim Jong Un to be its general secretary, state media report. The announcement by the rubber-stamp party congress on Sunday comes as little surprise given the Kim family has ruled the dictatorship since the late 1940s. State-run KCNA said that under Kim's leadership North Korea "radically improved" its "war deterrence", "with the nuclear forces as its pivot". Despite long-standing international sanctions, North Korea has continued to build its nuclear capabilities, regularly testing banned intercontinental missiles. But the secrecy of the regime makes it harder to evaluate how much progress the military has made. Kim, who took over control of the regime after his father's death in 2011, has invested heavily in the nuclear weapons programme, turning Pyongyang into a far bigger challenge for the West, and especially the US. He is expected to announce the next phase of the country's weapons programme during the congress, which is now in its fourth day.…