Would it surprise anyone to know that Yemen was also once a colony of the Brits?
And because they maneuvered Wahhabi Saudis into a position of power, the Saudis thought they could do whatever in the area. This led to a conflict with Yemen, already in the 1930s:

"Capitalizing on the Yemen government weakness, the Saudi rulers in 1934, split the three provinces from Yemen and annexed them to their territory, according to Taif agreement [i.e., Asir, Jizan, and Najran]. The accord should be extended every 20 years. The last time extension was in 1974 by Yemeni coup leader Ibrahim al-Hamdi. Saudi Arabia has no international legitimacy to continue its control over the three Yemeni provinces. Sana’a can advance its goal to take back during war conditions the provinces taking advantage of the discontentment of the Shiites of these provinces who are suffering from systematic discrimination, injustice, suppression, and demographic change policies. In other words, while the Saudis are insisting on a fruitless war in Yemen, the Yemenis can retake their occupied provinces with more favorable conditions than those of negotiations at a time of peace."

From 2021: https://thewarsan.com/does-houthis-seek-taking-back-occupied-yemeni-territories-from-saudi-arabia/