The Houthi capture of Sana'a in 2014 relied on a secret alliance with former dictator Ali Abdullah Saleh. Security forces did not oppose the rebels, and many officers joined them instead. Nadwa Al-Dawsari said, "the Houthis had been repeatedly underestimated." This mistake continues to shape how many view the group.

Your analysis piece on the Houthi campaign against Saudi Arabia ("Latest Houthi escalation puts focus on rebels' strategic aims", Report, October 19) traces the movement's path from rebellion against the government of Yemeni dictator Ali Abdullah Saleh to the capture of Sana'a in 2014. Yet it passes over the alliance that made the capture possible.

By May 2014, while serving in Sana'a with the EU, I was describing a Houthi bellicosity without precedent, and the alliance with Saleh explains much of it.

As a 2018 study for Oxford Research Group by Jack Watling and Namir Shabibi, to which I contributed, records, Saleh's Republican Guard had been broken up only on paper and its officers stayed loyal to the Yemeni ruler. When the Houthis entered the capital, the security forces that America and Britain had mentored at close quarters since the attack on the USS Cole, did not oppose them. Indeed, a number of former Republican Guards went over to the rebel side, and a senior officer of the British-trained National Security Bureau went on to run the bureau for the Houthis.

Nadwa Al-Dawsari, an author and Yemen expert, told the US House Foreign Affairs Committee in September that the Houthis had been repeatedly underestimated.

The habit began in 2014, when it was convenient to see a sectarian insurgency on the margins and to overlook the state apparatus that came over to it. But calling the Houthis "a radical brand of Zaydism" repeats that mistake.