The threat that Houthi militants pose by conducting incursions into Saudi Arabia is more than a military concern; it also has a massive effect on the perception of the success of Saudi military capability when it comes to dealing with the Yemen crisis. These are not the first clashes between Saudi forces and Houthi combatants on the Saudi side of the border during the crisis. But the proximity of fighting to population centers and the use of mortar and rocket artillery fire has elevated the impact of recent attacks. Not only does the inability to shield the kingdom from attacks risk influencing public support for the Yemen operation, but it also endangers the position of the Saudi leaders responsible for running the military campaign. In the context of the current power struggle, the perception of success is critical.
From the Houthi perspective, incursions across the Saudi border follow a time when their major offensive movements across Yemen have been significantly interdicted by Saudi-led coalition air operations. The Houthis have perhaps realized that they are approaching the limits of their ability to gain territory. If this is their mindset, the launching of attacks on the Saudi cities of Najran and toward Jizan makes sense. The aggression increases pressure on Riyadh to either negotiate or launch a ground incursion into Yemen.
If the Houthis feel they are unable to make further gains, a cease-fire could be a way to solidify what they have achieved so far — before either a counteroffensive or negotiations weaken their position. On the other hand, forcing Riyadh to conduct a ground incursion would result in Saudi casualties, because Saudi forces would not be as invulnerable as they have been from the air. At the very least, the border incursions have already caused Saudi Arabia to focus its air campaign on the border region, greatly reducing pressure on the Houthi operations in southern areas such as the city of Aden, where they could now gain more freedom of movement.
Even if Saudi Arabia does conduct a ground incursion into Yemen, it would be a limited operation staying close to the Saudi border. Such an operation could include the razing of several villages located in this border area that have been used by Houthi fighters to launch attacks against Saudi Arabia. Already the Saudi air force has been pounding the Sadah border region and calling for civilians to abandon the area. If these air operations fail to halt Houthi attacks against Saudi Arabia, and a cease-fire does not come through, a ground incursion — and all the risk it entails — could become the Saudis' only viable option to maintain the perception of success of their military operations in Yemen.
However, Riyadh's ground forces have always been located within reach of the border and have established solid defensive positions. An offensive would take them out of those positions and cause them to traverse complex and rough terrain, exposing themselves to Houthi counterattacks. Attempts to secure foreign military assistance for a ground incursion have also been unsuccessful, with Egypt and Pakistan's refusals to grant troops being most notable. The smaller troop contributions promised by Sudan and Senegal would not be sufficient to carry such an operation or to even lighten the burden for Saudi Arabia significantly.
While the success of the cease-fire is not guaranteed, the conduct of the military campaign and the current situation in Yemen shows that an ultimate resolution of the current crisis will not be possible solely through military means, especially with the Saudis trying to use as limited a military force as possible. The negotiation process will be critical, and the current constraints imposed on both sides by each other seem to indicate the time is ripe for this process to begin.
Of course, the humanitarian cease-fire could be nothing more than a temporary pause in hostilities, but given the context and timing, it could open up opportunities for longer lasting negotiated terms. Sources have already suggested that the United States has been trying to convince Saudi Arabia of the need for a cease-fire, allegedly influenced by Iranian requests within the U.S.-Iran negotiations. At the same time, reports have emerged that Saudi Arabia has dropped the requirement for negotiations to take place in Riyadh — something al-Houthi leaders had opposed — and would agree to negotiating on neutral grounds in Geneva. All of these indications, along with the constraints on the battlefield, suggest that the critical point has come where a cease-fire and negotiations could serve both parties' interests.