> The idea that allied nations don't maintain strategic autonomy with respect to each other is very modern.
No it's not. The point of making an alliance is that you're not stuck with strategic autonomy. You can tell other people that if they mess with you, they're also messing with whoever you're allied with. If you were autonomous, that wouldn't be true.
Again, that's a very modern perspective. When Portugal faced colonial revolts in the 1960s and early 1970s, NATO didn't help at all, and some members including the United States actively hoped Portugal would lose and free their colonies. Nor did they help France in the Algerian War. (The terms of the NATO treaty anticipated these conflicts, formally excluding all territory outside of Europe and North America from collective defense obligations so there'd be no question that help wouldn't come.)
Again, not being autonomous is the purpose of an alliance. It's the only purpose, and this is just as true of NATO-at-inception as it is of everything else. Portugal and France didn't get the ability to tell their own citizens that making trouble would get them squished by the United States. But they did get the ability to tell Spain that.
If you wanted to be strategically autonomous, you wouldn't have to do anything, because that's how you start out.
No it's not. The point of making an alliance is that you're not stuck with strategic autonomy. You can tell other people that if they mess with you, they're also messing with whoever you're allied with. If you were autonomous, that wouldn't be true.