Yemen is located on the southwest corner of the Arabian Peninsula, across from the Horn of Africa. With Saudi Arabia to the north and Oman to the east, Yemen’s land borders are largely isolated by the Empty Quarter, a vast, uninhabited desert that stretches through the region. Across the Red Sea, Ethiopia, Eritrea, Djibouti and Somalia are linked to Yemen by trade, religion and culture. From its vantage point on the Red Sea and the Gulf of Aden, Yemen overlooks one of the world’s biggest trade routes. Yemen has three geographic regions: the northern and western highlands, anchored by the capital Sanaa; the southern coastal harbors around Aden; and the eastern desert of the Hadramawt. For most of its history, the country’s civilization centered on the highlands, where enough rain falls to sustain agriculture. Because they lack oil and mineral resources, Yemen’s highlands are dependent on these farmlands. Meanwhile coastal harbor cities like Aden survived off trade and piracy, while the desert interior developed a Bedouin trading and raiding culture that siphoned wealth from the two nearby regions. Dwindling water supplies threaten this balance, however, as skyrocketing populations and shifting agricultural practices strain the demographic sustainability of the highlands. Nearly 20 million of Yemen’s 26.8 million people live in or near the highlands, which envelop and isolate Sanaa. So for outside powers, ports along the Red Sea trade routes of the south tend to make for better targets than the Yemeni capital. Throughout history, states from Rome to Great Britain have tried to capture Aden and its environs. The vulnerability of the city and its southern surroundings to foreign influence and meddling has repeatedly opened rifts between Yemen’s north and south. During these times of tension, the Hadramawt east often slips from the grasp of the central government. Yemen’s geographic challenges, then, are threefold. First, the country must ward off foreign encroachment on its exposed southern flank. Second, it must find a way to manage its increasingly scarce resources. And third, Sanaa must keep the Hadramawt -- known for its ability to threaten national unity -- under tight control.