Cheng Li-wun, chairperson of Taiwan's opposition Kuomintang party, arrived in China for a landmark six-day visit at the invitation of President Xi Jinping.This trip marks the first time a sitting leader of the party has visited the mainland in a decade to restart frozen dialogue.The peace mission coincides with intense debate in Taiwan over a $40 billion defense budget intended to purchase weapons from the USA.Government officials in Taipei warned that the visit must not undermine national security or legitimate international defense cooperation.