The Houthis can't control all of Yemen. They are a sectarian group in a heavily armed society - and their ideology is rejected by a large portion of Yemenis.
They have failed to build socio-political alliances & have lost past alliances. Tribal alliances in the north have eroded.
Even if the Houthis expanded militarily it can't sustain. They never speak about sharing power with other Yemenis.
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