Why was Japan able to thrive after the atomic bombs without serious radiation issues for a long time? /u/pokemon-sucks No such thing as stupid questions

Watching a video on youtube that is talking about a scenario between North Korea and South Korea. The narrator said that the “fallout” would “render the peninsula radioactive for decades, perhaps century’s”. So, was it the type of nukes the US used on Japan that caused it not to be all radioactive for a long time or is it the newer stuff that either NK or SK would use?

Watching a video on youtube that is talking about a scenario between North Korea and South Korea. The narrator said that the “fallout” would “render the peninsula radioactive for decades, perhaps century’s”. So, was it the type of nukes the US used on Japan that caused it not to be all radioactive for a long time or is it the newer stuff that either NK or SK would use?