text: Tachi swords were notably ineffective against the leather armor worn by these people.
full_question: Tachi swords were notably ineffective against the leather armor worn by these people. Interactions with these people inspired the construction of a "Borui" stone wall, whose placement led to the battle of Koan. These people departed from Masan and were able to seize Iki and Tsushima during an expedition where they were repelled at Hakata Bay. An inability to pay the Samurai who fought these people presaged the downfall of the Kamakura shogunate. Kamikaze typhoons thwarted two attempted invasions of Japan by, for 10 points, what people under Kublai Khan?
first_sentence: Tachi swords were notably ineffective against the leather armor worn by these people.