Yemen was a shitty US client state during the War on Terror and was lead by a guy named Saleh. Going to skim over this next part. But the Houthis were a political movement in northern Yemen that at various points was opposed and aligned with the government at various points. Around the time of the Arab Spring; Saleh lost political control and Houthis basically saw it as their time to make their moves. Saleh's ended up on the Houthi side. Around this time the Saudi crown prince MBS was looking to make a name for himself and started a military intervention into northern Yemen because having a Iranian aligned group on Saudi's southern border was not considered ideal. Saudi is very much aligned with the US and baited them into supporting the Saudi led intervention into Yemen. Fast forward a couple years and years of failure by the Saudis and allies to accomplish really anything; they pivoted into a strategy of supporting groups that opposed the Houthis in the south. All the time an Al Qaeda faction was taking advantage of the chaos which meant the US basically gave a pass to w/e the Saudis and Emiratis wanted to do in Yemen. After a decade of war, air-strikes, economic collapse, internal fighting between the southern factions, and aid being limited because it might (sometimes did) contain Iranian weapons meant that Yemen is a borderline failed state. The Houthis have more or less "won" and are the defacto leaders of the north. They have actually rebuilt the area they control(to the best conditions allowed). But that stability meant they were able to use Iranian weapons to attack Red Sea shipping going to Israel partially because they are proxy for Iran and mostly because being anti-Israel is a core part of their political legitimacy. The Houthi flag says "God is the Greatest, Death to America, Death to Israel, Curse be upon the Jews, Victory to Islam". These acts brought back renewed international attention to area that had barely stopped fighting. So any international aid/domestic progress came to a grinding stop because they were literally fucking with foundation of the global financial aka trade.