Even for long-time watchers of the Middle East like myself, the region's enmities and alliances have become very difficult to keep track of.

This has just been taken to a mind-bogglingly new level by Saudi Arabia's decision to launch a military campaign in Yemen against the Houthi movement.

Last September the Houthis, backed by Yemen's deposed president, Ali Abdullah Saleh (whom the Houthis fought against in 2009), stormed the Yemeni capital Sana'a. Since then they have captured large parts of the country, forcing President Abd Rabbuh Mansur Hadi to flee to the southern city of Aden.

The Houthis are Zaidi Shia, and are seen as closely aligned with Iran, which is a key reason why the Saudis, backed by other Gulf allies and seemingly by the US, have now intervened. But the Houthis are also fighting al Qaeda elements and Islamic State supporters in Yemen.

So in Iraq and Syria, the US, backed by Saudi Arabia (at least nominally), is fighting against al Qaeda and Islamic State, and both groups are also being fought by Iran. But in Yemen, Saudi Arabia, backed by the US, is fighting against the Houthis, who are supported by Iran but who are fighting al Qaeda and Islamic State. 

Confused? So am I.