When South Korea and the United States amended their missile guidelines last month after years of tough negotiations, China and other countries expressed some concerns about the revisions, the first change in the guidelines in more than a decade. Shedding some light on the reasons for the decision might help assuage them. Under a 2001 accord with Washington, Seoul agreed not to deploy ballistic missiles having a range of more than 300 km or a payload of more than 500 kg. Under the new guidelines, South Korea can now possess ballistic missiles with a range up to 800 kilometers with a higher maximum payload of 500 kilograms. The payloads can be even heavier for missiles with shorter ranges. The agreement also permits the ROK to operate drone aircraft having a range of 300 km with payloads up to 2,500 kilograms as well as shorter-range UAVs with no restrictions on their payloads.