Saudi Arabia's campaign to stop the Houthis from ruling over Yemen could define its role in the Middle East for years and shape its regional struggle with the rebels' ally Iran.

Success will establish Riyadh as de facto leader of the region's Sunni states it has pulled together in a complex armed operation, and embolden it to pursue a more assertive stance against what it sees as the expansionist ambitions of its archrival, Shiite Iran, in Iraq, Syria, Lebanon and Bahrain.

But failure could hamper Riyadh's ability to persuade allies and neighbors to join it in future ventures and deal a public setback to its new monarch, King Salman bin Abdul-Aziz al-Saud, as well as other senior princes early in his reign.