Once again we see "blowback" in action. Here's the cycle:
1. A major power backs a side in an internal struggle for their own end. If necessary, a conflict is manufactured by propping up rebels, a coup, etc;
2. The other side, which tends to be the internally popular side, resists. Because of that popular support, they can survive, thrive and grow;
3. Insurgencies are incredibly effective. Counter-insurgencies are incredibly difficult. The insurgents are fighting for their lives. The boots on the ground for the major power backed forces don't tend to want to be there;
4. Reactionary forces are seen by the besieged populace as emancipatory forces;
5. When the resolve of the major power breaks or there is simply a policy shift, the unpopular government crumbles and is replaced by those reactionary forces. Classic example: the fundamentalist Iranian revolution of 1979. Go and look at what Iran was like before the 1953 coup.
6. Those former insurgents become a regional thorn in the side for that major power for decades to come;
7. The major power, unwilling to commit militarily, responds with economic sanctions. This does little more than starve people and kill people due to lack of medicine. But th eregime survives. It can even be strengthened as the citizens blame the major power for their plight.
The Saudis committed genocide in Yemen. For years. And the world ignored it. They used US-supplied weapons to do it. At any time, the US could've ended Saudi atrocities in Yemen with a phone call.
And now the Houthi rebels have become battle-hardened guerillas and insurgents, capable of projecting force into the vital shipping lanes of the Red Sea. Drones have become incredibly cheap, to the point that a ragtag group will tie up a US carrier group who will try to enforce security, much like they have done with, say, Somali pirates.
The US carrier group may even adequately suppress the Houthis but this is attrition and Houthi investment is a drop in the ocean compared to the cost to the US.
The last two decades saw a massive change in drone use by the military. It was always just a matter of time before that military technology filtered down to insurgents and it's going to have a massive effect.
We saw this in Afghanistan in the 1970s when US-supplied Stinger missiles completely changed the battlefield as they rendered Soviet gunships ineffective at an incredibly low cost.
This isn't a statement supporting the Houthis (or even denoucning them). It's simply an analysis of the pattern that has played out many times, particularly since WW2.
This is what I mean by "blowback".