Concept:The UNO is judged successful mainly by its role in preventing another world war and maintaining international peace.Explanation:The United Nations was founded after World War II with the key goal of saving future generations from the horrors of war.It has served as a global forum for peaceful negotiation and collective security.Its primary achievement is widely seen as preventing the outbreak of another world war.The other options, such as increasing membership or acquiring nuclear power, do not represent the fundamental purpose of the UNO.Answer:B. of its control of outbreak of another world war.