Complex sentence: Ryukyuan missions to Joseon were diplomatic and trade ventures of the Ryūkyū Kingdom which were intermittently sent in the years 1392-1879, representing a significant aspect of the international relations of mutual Ryukyuan-Joseon contacts and communication.
Split into simpler sentences: Ryukyuan missions to Joseon were diplomatic and trade ventures of the Ryūkyū Kingdom which were intermittently sent in the years 1392-1879. These diplomatic contacts represented a significant aspect of the international relations of mutual Ryukyuan-Joseon contacts and communication.