A Five Great Countries Summit (五大国会談, Godaikoku Kaidan) is a formal gathering of the daimyō of the Five Great Shinobi Countries. Although the daimyō have different ways of contacting each other that they use when necessary, an actual Summit is incredibly rare; prior to Shikamaru Shinden, there hadn't been a Summit since the time of Shikamaru Nara's great-grandfather.
In Shikamaru Shinden, a Five Great Countries Summit is convened at the request of Ikkyū Madoka, the Land of Fire's daimyō, in response to the Land of Earth's plans to invade the Land of Flowers. Such an invasion would end the peace of the Shinobi Union that their respective country's hidden villages have established through years of hard work. The Earth's daimyō, Danjō, doesn't feel this should matter and that, if anything, the hidden villages should be grateful for the opportunity to rediscover what it means to be shinobi: death in battle. The Land of Lightning's daimyō, Tekkan - whose country is allied with the Land of Flowers - feels this is poor justification for war, but he and Danjō are unable to reach a compromise.
Because Danjō desires the Land of Flowers' fertile lands, Ikkyū proposes turning over some of the Land of Fire's territory to the Land of Earth as a compromise; the offered lands previously belonged to the Land of Earth, so its inhabitants would not protest. Danjō dislikes the idea because he's already invested a great deal of money in the invasion and doesn't want it to go to waste. Such a transfer of lands would require the approval of the surrounding countries anyway, so Ikkyū suggests letting the Land of Flowers' fate be decided at the first ever Continental Summit. Tekkan, the Wind daimyō, and Water daimyō approve of this. When Danjō continues to dither, Ikkyū raises another option: war between the Lands of Fire and Earth. Danjō finally agrees.