Yeman was always a single country until Iran urged the Houthis, Shi'ites, to break away from the government, Sunni. The Houthis were successful in capturing much of Yemen before signing a peace agreement with the government. More recently, Iran urged the Houthis to break the agreement and try to capture all of Yemen with Iran's help. Saudi Arabia is helping the government to hold off the Houthi/Iranian attack. Look around the ME, Iran has done this same thing in Lebanon, now more of an Iranian province that a sovereign state, in Syria, now a failed state being exploited by Iran to further its own imperialist ambitions, and in Iraq, which Obama gifted to Iran when he withdrew our troops. Wars are raging across the ME and in every one of them Iran is supporting Shi'ites against Sunni. Without Iran, none of these wars would be happening.