Saudi Arabia–Yemen relations
Saudi Arabia and Yemen relations refers to the current and historical relationship between Saudi Arabia and Yemen. The two countries generally enjoy good relations and closely cooperate in military, economic and cultural issues. Saudi Arabia has two main goals in Yemen 
- Riyadh seeks to prevent any form of Yemen unity. A united strong Yemen could end the Saudi dominance over the Arabian peninsula.
- Saudi Arabia works to prevent powers from establishing bases of influence in Yemen. Riyadh would prefer all states in the Arabian peninsula share its monarchical form of government.
The Modern History of Yemeni - Saudi relationship begins in 1803 with an attack by Saudi forces of the territory of zaydi imamate with the help of some local Yemeni tribes. The Saudis won and had control over the Tihama region until 1818 when the forces of Mohammed Ali Pasha destroyed the Saudi state  The establishment of a protectorate over the Idrisi sultanate in Asir led to clasehs between Ibn saud and imam Yahya of Yemen. Ibn Saud captured Asir and Jizan while the imam managed to occupy the oasis of Najran Negotiations proved fruitless, the Saudis regained control over Najran and occupied about 100 kilometers of coastal plain  In the Saudi-Yemeni treaty of 1934, which was signed and ratified shortly after the war, Yemen recognized the incorporation of the Asir into Saudi Arabia. This treaty, however, had an unusual feature: its provisions were only valid for a 20-year renewable term. The treaty was apparently renewed in 1954. In 1974, Saudi Arabia wanted North Yemen to agree to make the border demarcation permanent and not subject to further renewal every 20 years. The North Yemeni prime minister at the time signed an agreement to this effect, but it proved so politically unpopular within Yemen that his government was unable to ratify it. The 1934 treaty only defined North Yemen's northern border with Saudi Arabia. Neither North Yemen's eastern border nor South Yemen's northern border with it were ever defined.
in 1948, Saudi Arabia provided aid to imam Ahmed fearing the "constitutional" nature of an uprising in Yemen 
Yemen Civil War
Saudi-Yemeni relations were considerably strained as a result of the 1962 revolution, which ousted the Yemeni royal family, and the ensuing civil war between republican and royalist forces which lasted until 1970. Egypt's Nasser strongly supported the newly declared Yemen Arab Republic and sent Egyptian troops to prevent it from being overwhelmed by the royalists. The Saudi government saw these events not only as a threat to its influence in a neighboring country but as a threat to the continuation of monarchial rule in Saudi Arabia itself. Nasser made no secret of his desire to see all Arab monarchies overthrown and united in a pan-Arab "republic" under his leadership. Saudi Arabia, in response, provided substantial military assistance to the royalist forces seeking to destroy the republic.
Although bitter enemies during much of the 1960s, Saudi Arabia and North Yemen became increasingly cooperative after the withdrawal of Egyptian troops, the coming to power of a more conservative government in Sana'a, and the realization that they faced a common threat from the Soviet backed Marxist regime that arose in South Yemen following Britain's withdrawal in 1967. Saudi Arabia feared that the Marxist regime in the South would subvert and gain control over the North as well. South Yemen threatened Saudi Arabia in other ways too. South Yemen transformed the ongoing regional rebellion in Oman's Dhofar province (bordering South Yemen) into an insurgency seeking to replace British-backed monarchies with Marxist rule in Oman, the United Arab Emirates, Qatar and Bahrain. Saudi Arabia also sponsored several efforts to overthrow the Marxist regime from South Yemen or dismember the country.
In addition, there were serious clashes along the undefined Saudi-South-Yemeni border. In order to protect itself, then, Saudi Arabia stopped supporting royalist forces opposing the North Yemeni government and gave Sanaa military and economic aid in order to strengthen the North relative to the South." Yet even at the height of Saudi-North-Yemeni cooperation, which occurred during the 1970s, the way in which Riyadh aided Sanaa became a source of contention.
There were frequent Yemeni claims of Saudi troop movements in the frontier area. These usually coincided with periods of tension or new diplomatic moves on the border question. In October 1990, Saudi Arabia announced plans to construct a multi-billion dollar “military city” near Jizan at the north-western end of the border. This was to be one of a series in strategic areas, designed to house 50,000 officers and men with their families, and was described by Saudi officials as “a fortified bastion at our gates”. In 1991 a Yemeni border post at Baq’ah in north-west Yemen was reported to have been captured by Saudi troops, though Riyadh denied this. A bizarre diplomatic incident occurred in May 1992 when a Saudi weather forecast appeared to claim that the Kharakhayr region of Hadramaut belonged to the kingdom. As this was the birthplace of Vice-President al-Baid, it resulted in a stiff protest note from Sana’a. Further complicating the issue, about the same time, the Saudis were reported to be offering Saudi citizenship to some traditionally Yemeni border tribes in Shabwa, Hadramaut and Al-Mahara provinces.
- Saudi-Yemeni Relations: Domestic Structures and Foreign Influence By F. Gregory Gause p.4 ISBN 978-0-231-07044-7 Columbia University Press
- Saudi-Yemeni Relations: Domestic Structures and Foreign Influence By F. Gregory Gause p.57
- Saudi-Yemeni Relations: Domestic Structures and Foreign Influence By F. Gregory Gause p.58
- A History of Modern Yemen By Paul Dresch 35
- British and Foreign State Papers. 1934 (London: HMSO, 1939), pp. 670-683.
- Gause. pp. 105-06.
- Saudi-Yemeni Relations: Domestic Structures and Foreign Influence By F. Gregory Gause 58
- Malcolm H. Kerr, The Arab Cold War, 3rd ed. (Oxford: Oxford University Press, 1971), pp. 107-14
- Agence France Presse, 8 October 1990, and Reuter, 3 June 1992
- Associated Press, 9 October 1990
- BBC Monitoring Service, 16 April 1991
- Agence France Presse, 24 May 1992
- Reuter, 3 June 1992