The case of one region with multiple countries is a strange case indeed. It is a strong weakening point and problem-causing for the whole region in general and to each separate country in particular. It leads to different and opposing interests instead of one joint interest.
The divided Arab region embodies such political illiteracy aside from selfishness and ruthlessness which contradicts the Islamic instructions and human values.
The European Union, as an example, had undergone a lot of wars; the most horrifying being the first and second World Wars which witnessed human massacres, however, Europeans realized that the reason of these loses and wars lied on contradicting advantages and interests of their countries. Therefore, they made radical solutions for these disputes via establishing a Joint European Market that ended all their disagreements and found them a common interest. It has now a developed European Union which works through a step-by-step strategy to becoming one united country.

Arab-Arab Relations;
Since Sykes-Picot Agreement, Arab nation have been divided into small countries, the relations between these countries have been based on contradictory mottos, disconnection and media wars. Today, we clearly see this disagreement in relations like the one between Algeria-Morocco and the Iraqi-Syrian case which are both symbols of the Arab-Arab relations as a whole.

Yemen & KSA strategic depth
The concept of strategic depth likely come from military affairs then enlarged to cover up other points. If one country for example, is exposed to a foreign military attack or an internal crisis, the other neighboring country becomes either a supportive side for its neighbor by providing free military movements on its land or be unsupportive by fuelling crises or assists the internal enemy. It is also associated with national security, economy, and trafficking and other issues.
In this regard, Yemen represents the most significant strategic depth for KSA and vis versa. However, both countries do not have strong relations and always fall in fatal strategic errors.

KSA Errors
KSA has made unwarranted strategic errors in its relations with its neighboring country, Yemen. These errors have consequently impacted the Saudi national security, as well as Arab and Islamic national security as a whole. The most apparent error has been that Saudi’s policy towards Yemen is based on a myth that says,” a weak Yemen means a strong KSA and a strong Yemen means a weak KSA.” If this myth has been tested by scientific study it would show the opposite and would clearly show that the strength of one is strength for all.
This motive towards Yemen is clearly embodied in different stances adopted by KSA. It, for example, publicly supported the separatists in the 1994 war. It took punishment measures against Yemeni residents because of the Yemen official stance in the first Gulf War. Another example of a weakening policy towards Yemen is the exporting of Salafi Ideology in the wake of extended Iranian strategy in the region. Instead of supporting education in Yemen which is set up of non-sectarian trends, it exported the Salafi Ideology to face the Shite extension in Yemen through the Zaidi Sect. However, the policy failed and Salafis instead of blocking the Shite spread had broken the Sunni line and underwent arguments with other Sunnis.

Yemeni errors
On the other hand, Yemen has mistakenly made false decisions in regards with KSA relations. It supported the Iraqi stance in the first Gulf War and lost its relations with KSA and did not even benefit the Iraqis.
The Yemeni regime is not considerably aware of dealing with opposing parties in foreign policy area. It is either a free follower as its unjustified withdraw from Gaza Summit in Doha or with its far and Anti-Saudi Regime relations such as the Iranian and Libyan relations.
The Yemeni authority also lacks institutional decision-making. It fails to make relations with other countries based on competitiveness, reliability and exchanged advantages.

How the relations should look like…?
Both countries should coordinate on the factors and elements of strength. The KSA, a rich oil resourced country, is in need of a safe and friendly neighbor like Yemen; as it has huge human resources and is a large market for Saudi products.
The Saudi policy towards Yemen should be based on reliability and open support for Yemen’s multiplicity of political parties and trends.
KSA should consider the stability of Yemen as a part of its national security.