In a way, this Antares launch is the end to a period of in spaceflight that began in 1991, with the collapse of the Soviet Union.
With the USSR gone, the former Soviet aerospace industry was a wreck, to say the absolute least of it, as all the former state-owned Design Bureaus found themselves scattered across several states, not to mention extremely short on funding.
In short, this scared the US State Department, because Oh No! All the talented folks who know how to build rocket might get poached by [INSERT CONTEMPORARY US ADVERSARY HERE] to build nuclear missiles for them! We Cannot Allow This!
The scattered aerospace industry being broke ALSO meant they were cheap to work with, in a lot of cases, so these two factors combined would bring about a whole new era of international collaboration in spaceflight.
It was the era that brought us Shuttle flights to the Mir space station. It gave us the International Space Station, as NASA ripped out half of Space Station Freedom to fuse with the Russian Mir-2
It gave us SeaLaunch, where Boeing partnered with two former Soviet Design Bureaus to launch the Zenit rocket from an offshore platform. Remember Zenit, it'll become relevant again later.
And, relevant to the matter at hand, it gave us several great instances of Russian engines on American rockets.
This one's a long one, i had to draft it twice because it was too long the first time, and I wasn't gonna do that a third time so here we go. Beware. There's history below the cut.