I don't understand why you don't want them to get advanced (or think US leaders). Economics is not a zero sum game. More developed states are good for us. If these states start to increase their oil production, its good for us.

Also I don't know what advanced threads you think they could become? Other then becoming nuclear powers, they can not pose such a thread. Non of the countries that the US attacked is anywhere close to that level.

The only country that is, Iran, was not attacked by the US and are voluntary not building a nuke.

Also the chaos the created is totally against their interest, now china is a major player in Iraqi oil. Russia and Iran are drawing together more over the Syria issue. They are running into a huge conflict of interest regarding the Turks and the Kurds. That's just the beginning this strategic disaster.

Its far easier to deal with stable regimes and when you want to take one down, you should always have a successor in mind. You can go threw history and look at all the great conqueror in history, they are always trying to set up puppet regimes that they control, and not throw everything into chaos.

You don't need to be that "advanced" to cause real trouble to other countries around the world, and strong countries generally have more stake in the international and are less likely to rock the boat, which in turn favors other strong, status quo powers. From the US point of view, Putin isn't a friendly guy, but today's Russia is far better for the US than a weak, divided one full of Russian Orthodox extremist groups bent on exporting the traditionalist revolution across the world. Likewise, it's not like even the strongest possible Syria would pose a "real problem" for the likes of US, Russia, the EU or China.