Background on Saudi-Yemen relations

This is not the first time Saudi Arabia has bombed the Houthis in Yemen. As Brian Whitaker explains in a blog post the Kingdom has a long and messy history with the Shiite rebel group from Yemen's north.

Almost constantly since its foundation in 1932, Saudi Arabia has been involved in Yemen politically, and sometimes militarily – often with negative consequences for Yemen

In the most recent episode of fighting (2009-10), which the government called Operation Scorched Earth, the conflict became internationalised when Saudi Arabia carried out bombing raids in Yemen with President Saleh's blessing. 

Details are still obscure because journalists and aid workers were not allowed into the area but that thousands were killed or injured and an estimated 350,000 were forced to leave their homes.

Saudi interests are best served by keeping Yemen “on the wobble” (as one western diplomat put it) – though not so wobbly that regional stability is jeopardised. Before the unification of north and south Yemen in 1990, this amounted to ensuring that both parts of the country focused their attentions on each other rather than on their non-Yemeni neighbours.