Sources

Helpful links: 

https://travel.state.gov/content/passports/en/alertswarnings/north-korea-travel-warning.html

https://jp.usembassy.gov/

https://kr.usembassy.gov/

https://china.usembassy-china.org.cn/

Sources (includes links above): 

https://cpj.org/2015/04/10-most-censored-countries.php

https://freedomhouse.org/report/freedom-world/2016/japan

https://freedomhouse.org/report/freedom-world/2017/china

https://freedomhouse.org/report/freedom-world/2016/north-korea

http://www.bbc.com/news/world-asia-pacific-15289563

Credits: Jay Perez is the sole contributor to East Asian Borders. Jay is the lead researcher, programmer, and organizer.