Introduction

In 2017 Saudi Arabia defends its southern border with thousands of heavily armed troops and a Patriot anti-ballistic missile defense system. Yet until quite recently, Riyadh looked upon this border area with only passing interest. Disagreement over the demarcation of the boundary was an important feature of Saudi-Yemeni relations during the twentieth century, but neither government saw the need to manage cross-border movements. Tribes and communities that straddle both sides continued to trade and interact as if Ibn Saud had never wrested the provinces of Asir, Najran and Jizan from the Yemeni Imamate in the early 1930s. By the turn of the millennium, Riyadh increasingly came to see its national security threatened by transnational clandestine actors – principally terrorists, illegal migrants and smugglers of illicit items. This perceived new security paradigm recast Saudi Arabia's thinking and behaviour towards its southern border.

Controlling borders, as distinct from defending borders, is about restricting territorial access. States employ a variety of physical, technical and administrative measures to regulate what and who enters their space. Since the early 2000s, Saudi Arabia attempted to implement such measures at its borders with Iraq and Yemen. The Yemeni government's inability jointly to manage the border impelled Saudi Arabia to pursue an increasingly unilateral and interventionist policy at and beyond the border. This chapter will show that regulating access to Saudi territory from Yemen fueled a shadow economy in northern Yemen, distorting local power dynamics. In the mountainous borderlands that characterize much of the terrain between the Empty Quarter and the Red Sea, smugglers, rogue military units and, where they existed, corrupt officials have profited from clandestine trade.

Saudi Arabia considered the presence of ungoverned space beyond its southern border a vulnerability before the Huthis and their allies seized power. Indeed, it was fear that growing lawlessness in northern Yemen would spill over into Saudi Arabia that led to Riyadh's decision to intervene militarily in 2009-2010. Geopolitical rivalry with Iran was likely the leading factor in Saudi Arabia's decision in 2015 for direct military action in the Yemen conflict; but the need to seal the border to stop fighting spreading into Saudi territory was also a pressing concern.

Conflict has redefined the Saudi-Yemeni border, both symbolically and materially. Aside from a small number of discussions about the Yemeni-Saudi negotiations over the contested boundary, no attempt has been made to explain the transition of the border from a largely porous frontier into a defended border. This chapter addresses this omission. In doing so, it contributes to current discussions in the field of international relations about the relevance, or indeed irrelevance, of borders in dealing with transnational as opposed to inter-state problems.