The French expedition to Korea was an 1866 punitive expedition undertaken by the Second French Empire in retaliation for the earlier Korean execution of seven French Catholic missionaries. The encounter over Ganghwa Island lasted nearly six weeks. The result was an eventual French retreat, and a check on French influence in the region. The encounter also confirmed Korea in its isolationism for another decade, until Japan forced it to open up to trade in 1876 through the Treaty of Ganghwa.