South Korea's president has asked its northern neighbour not to cancel reunions of families divided by the war. North Korea has threatened to do so in protest of the upcoming US-South Korea military exercices. The bolstering of US forces acts both as a demonstration that South Korea is getting value for the $850mn a year it pays the US military; and as an added deterrent to North Korea. Al Jazeera's Harry Fawcett reports from the port of Busan.