Narendra III is the site of a Klingon outpost whose defence by the Enterprise-C helped forge peace between the Klingons and the Federation.
Narendra III hosted a Klingon outpost that came under Romulan attack. In Yesterday's Enterprise the Enterprise-C, under Captain Rachel Garrett, answered its distress call and was attacked by Romulan warships, and a rift threw the ship into the future.
Without the Enterprise-C's sacrifice at Narendra III, history changed and the Klingons and the Federation went to war. When the ship returned to its own time to fight, the honour shown by a Federation crew defending a Klingon world helped build the later alliance between the two powers.