National Socialism and Japanese Imperialism no longer exist, therefore they are no longer a threat to the world.
Communism does still exist, and is far more dangerous than it was in the 1950's and 1960's. Radical fundamentalist Islam also exists, even though we were engaged in a 20-year war against it. So we haven't really won a major war since World War Two. Consider also that World War Two was won in only five years. We've been plagued by Communism for about 73 years, and radical Islam for at least 20.