The Islamic Republic of Iran emerged as a major an effective player on the Yemeni scene during the last five years especially after the break out of the fourth war between the former Yemeni president and the Houthis in Saada.
With the breakout of the peaceful revolution against Saleh's regime in January last year, it seemed as if the Iranian role had retreated on the Yemeni scene, at the wake of the increase of the regional role on top of it the Saudi Kingdom, the international community and USA.
Iran seemed as if taking its breath to finish the final touches on the new role which it wants o play in post Saleh's Yemen. As the latter signed his departure decision in Riyadh on November 23, Tehran rushed in to work in an open way on the Yemeni scene, in a role neither its features nor its aims are not fully clear yet, however it is surely linked to the regional balance in the stage of the post Arab spring.
The Yemeni Iranian relations have passed through different stages of stability and disarray, whether during the split period or in the post unity era.
Following the 26 September revolution in 1962, and the establishment of the republican system in North Yemen, the late Iranian Shah Mohammed Reza Pahlavi, stood with a number of Arab countries with the Imam who was deposed by the revolution. It supported him all through the eight years of the civil war when the Yemeni people succeeded in imposing the republican system, and to achieve the national reconciliation. Sana'a started new relations with the countries that supported the Imam regime.
In 1975 late President Ibrahim al-Hamdi paid an official visit to Iran, where he received warm welcome by the Shah, however the southern Yemen's relations were not good with the Shah regime. 
Following the Islamic revolution in Iran in 1979 which deposed the Shah the Aden's relations with Iran improved, and further it became stronger with the breakout of the Iraqi Iranian war. The Sana'a relations with Tehran deteriorated , because of the clear support of President Ali Abdullah Saleh to Iraq in his war against Iran. The situation continued as it is until the restoration of unity in May 1990.
The Yemeni Iranian relations changed since then and began to improve following the death of Khomieni, and the shift of Iran from the revolution to the state's stage, led by Khamini' and Rafsangani, while the new united Yemen was looking for a an exit from their isolation, caused by its confused position because of the occupation of Iraq to Kuwait.
The Iranian Yemeni relations started to improve and the adoption of Yemen to the multiparty system encouraged Iran to enter into the Yemeni scene, where ideologically political currents had emerged, finding themselves closer to Iran. The latter found them capable of its support. They had provided to it by the lapse of time a real foothold for practicing its political influence.
This is what has actually happened, and appeared clearly with the beginning of the fourth war with the regime and the Houthis. For fifteen years, since 1990, Iran didn't provide real support to Yemen, as the ministerial committees used to hold annual meetings in Sana'a and Tehran consecutively, however Sana'a found no serious development or economic support from Tehran.
Despite the visit of President Saleh to Tehran in April 2000, and the visit of Khatami to Sana'a in May 2003, there were no real economic results to these relations.
Tehran remained keen on attracting Yemeni students to study in its (Hoza) religious schools, however their number remained to be limited. Most of them didn't return to Yemen, because they know that there is no opportunity for spreading the Ja'fari doctrine, which is not acceptable in Yemen.
By the end of the term of Mohammed Khatimi in 2005, who became a symbol for moderation, rationalism, realism and political maturity in the Iranian politics, the relations between the two countries deteriorated, because of the Iranian support to the Houthis in their fourth armed insurgence in 2007. The support emerged clearly in the sixth war when the Saudi war planes participated in bombing the Houthis positions, following the offensives that they launched against Saudi territories.
Saleh's regime continued on threatening with disclosing the Iranian support to the Houthis, however it did nothing in spite of the overt Iranian support.
After the end of the sixth war in 2010 because of the international pressure, Saleh's regime entered into the intensive care unit, being considered a regime on the verge of failure, until the popular peaceful revolution broke out in January 2011, that transferred it into the clinical death stage. It ended by removing the artificial breathing systems on last February 21 by electing Abdu Rabo Mansur Hadi as President.
The knowledge of Iran that Saleh's regime has departed made it to indulge strongly into the Yemeni scene, financially, politically and through media to be a major player, for their knowledge that the countries usually become weaker at their transitional stages.
The Yemeni people are exhausted and the state is almost about to disintegrate. There are huge vacuums that are being filled by al-Qaeda and the armed movements and Iran saw that it is appropriate to support her traditional Houthi allies and some of its new intellectual and leftist allies so as to fill some of the vacuums through the flow of money and by establishing satellite channels.
It also created confusion through some alliances which it knows that they would not continue and will stop sooner or later, when the money stops. It also knows that they will stop when the state's structure starts to pull together again and starts filling the vacuums filled by the fragile forces.
Iran knows that whatever the Yemeni weakness may be, it will not be its strategic playing field, because of the geographical proximity, the objection of the major forces and the opposition of the countries that monitor the transition process, and will not allow on the long term any Iranian role in Yemen so as to instigate sectarian, racist and doctrinal conflicts, while it is badly in need of stability and national unity.