Yemen presents a potent combination of problems for policy-makers confronting the prospect of state failure in this strategically important Red Sea country. It is the poorest state in the Arab world, with high levels of unemployment, rapid population growth and dwindling water resources.
President Saleh faces an intermittent civil war in the north, a southern separatist movement and resurgent terrorist groups. Yemen's jihadi networks appear to be growing as operating conditions in Iraq and Saudi Arabia become more difficult.
The underlying drivers for future instability are economic. The state budget is heavily dependent on revenue from dwindling oil supplies. Yemen's window of opportunity to shape its own future and create a post-oil economy is narrowing.
Western governments need to work towards an effective regional approach with the member states of the Gulf Cooperation Council, in particular Saudi Arabia.
Future instability in Yemen could expand a lawless zone stretching from northern Kenya, through Somalia and the Gulf of Aden, to Saudi Arabia. Piracy, organized crime and violent jihad would escalate, with implications for the security of shipping routes, the transit of oil through the Suez Canal and the internal security of Yemen's neighbours.