I don’t agree with the assessment, but in terms of a great power being very interested in the interests of a small country, consider Serbia and Russia before WWI.
I agree vassal is the wrong term... but we are currently committing global economic suicide on behalf of Israel's interests. I'm not sure what word is appropriate. Perhaps we need a new one.
While too big a subject to cover well here, the Serbia / Russia thing is different to US / Israel.
Primarily a Russia friendly Serbia was important for Russian trade routes (Black Sea to Mediterranean via the Dardanelles.) In other words geography made Serbia important.
In a twist on that theme, the strait of Hormuz is important to, well everyone, and we now see how geography can magnify a countries strategic value.
There were other factors which came into play with Russia. Ethnically Serbia was aligned with Russia - similar to the US / Israel relationship today.
It also didn't hurt that Russia at the time was experiencing internal discontent and this was a convenient way to thin the population, and get rid of malcontents. (Ironically would end up having the opposite effect of organizing, arming and training an army that ultimately would be instrumental in the revolution. )
The history leading up to ww1 is fascinating- so many players, all with really "big picture" goals, mostly with weak leadership.. Ultimately conflict was inevitable- if it hadn't been the arch-duke it would have been something else.
I'll look at Serbia, thank you.