Geopoliticalmonitor.com has followed the progress of the Shiite Houthi rebels very closely as they descended from the mountains in the north; sacked Sana’a and deposed the government of President Hadi; captured critical oil fields to the east of the capital; and marched southward towards Aden, the former capital of South Yemen where Hadi had taken refuge in the hope of mounting a counterattack.

Throughout the course of these events, it was an open question how Saudi Arabia would respond. Yemen, after all, with its near 50-50 split between Sunnis and Shiites and proximity to the Kingdom, represents fertile ground in the battle between Saudi Arabia and Iran – a rivalry that is increasingly unfettered as Washington experiments with a more balanced engagement in the region.

Well it seems we have our answer.

In our last situation report on Yemen, Geopoliticalmonitor.com predicted that the Houthis would push towards Aden in the hope of sacking the city before any coherent opposition could be organized, whether tribal or national. This is precisely what came to pass, as the Houthis stormed the al-Anad air base – which only days before had housed US commandos and support staff – capturing an estimated $500 million in US military equipment.

The al-Anad base is just 60km away from Aden, and unconfirmed reports yesterday put the rebels in and around the Aden airport.

Houthi forces within arm’s reach of the former president (who is now reported to have fled Aden) has spurred Saudi Arabia to action. In the name of protecting the “legitimate government of Yemen,” the Kingdom has announced a military campaign aimed at reversing the Houthis’ gains. Airstrikes have already started, with Sana’a’s airport and the al-Dulaimi military airbase being hit immediately after the announcement was made on Thursday.