 Complete the following phrase:  Following the Houthi takeover in Yemen, a border conflict erupted along the Yemeni-Saudi border. Saudi-backed forces attempted to advance into the Houthis core territories of northern Yemen, while pro-Houthi forces launched incursions into Saudi Arabia. Besides the general enmity between the Houthis and Saudi Arabia, the border conflict also takes place amid the still contentious issue where the border should be located in the first place. The southwestern Saudi Arabian province of Najran was traditionally part of Yemen until it was 