I don't know enough about Yemen to critique Reuters' piece, but here are a few highlights and my efforts to read between the lines
Reuters' International Crisis Group, in London, inform us that
The Houthis, like most tribesmen in Yemen's northern highlands, belong to the Zaidi sect of Shi'ite Islam, whose Hashemite line ruled for 1,000 years before the 1962 revolution.
It's worth noting that the U.S. offered of arms and equipment to Saudi Arabia, 1961, and the U.S. hosted a state dinner for King Saud in 1962. It's also worth noting the North Yemen civil war of 1962 - 1970. A military coup, seeking to over throw the royal dynasty and install a republic, was initiated by Nasser's Egypt, who had a variety of motives including including confronting imperialism in general and challenging British colonialism in the South Yemen port of Aden (the port where the USS Cole was bombed). Egypt was backed by the USSR.
On the other hand, Saudi Arabia, with U.S. backing, supported the long-ruling royalists. I believe monarchy was closely aligned with the Houthis tribesmen... who are now being associated with "rebels" in the Reuters piece, as follows:
The conflict [is] with the northern rebels, who complain of social, religious and economic discrimination in the southern Arabian state [of Yemen].
And, as often is the case, the Yemen government of Ali Abdullah Saleh is using the "war on terror" to paint the rebels with a broad brush:
After the September 11, 2001 attacks on U.S. cities, Saleh declared support for Washington's "war on terror," in part to enlist U.S. support against the Houthis, whom Yemeni officials accuse of having links to al Qaeda, Iran or Lebanon's Hezbollah.
My take, without deep research, is that the North Yemen "rebels" have legitimate grievances and President Saleh is probably a new, more modern "monarch"... yes, he was in the military until becoming president of North Yemen in 1978 (Saleh was suspected in the assassination of the previous president). He continued in the presidency after North and South Yemen were united in 1990... in other words, Saleh is a strong man, although like any good democracy, there are elections in Yemen.
So, there you have it.
1. Reuters, Factbox: Roots of Yemen's conflict with northern rebels, January, 2010.
2. US Presidential Papers Concerning Saudi Arabia 1941–1962.