The main island of Tsushima was once a single island but was divided into two in 1671 by the Ōfunakoshiseto canal and into three in 1900 by the Manzekiseto canal.
A illa principal de Tsushima foi unha única illa, pero dividíuse en dúas en 1671 pola canle Ōfunakoshiseto e en tres en 1900 pola canle Manzekiseto.