Passage: Tsushima Island (対馬, Tsushima) is an island of the Japanese archipelago situated in-between the Tsushima Strait and Korea Strait, approximately halfway between the Japanese mainland and the Korean Peninsula. 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. These canals were driven through isthmuses in the center of the island, creating "North Tsushima Island" (Kamijima) and "South Tsushima Island" (Shimojima). Tsushima also incorporates over 100 smaller islands (many tiny). The name Tsushima generally refers to all the islands collectively.

Question: What was the earliest year in which the island was separated?
1671