why did the Japanese close off their ports to the rest of the world to perry's voyage? why did they agree to trade with united states?

I'm not sure if this would be what your learning, but from my experience from living in Japan.

Japanese people believe the reason why they didn't try to get involved with other countries is because they didn't want any western influence. They only agreed to trade with Perry because they felt as though they were forced to, they were afraid of being invaded.