It was the most watched made for TV movie of all time. And, yes, it did affect the outcome of the Cold War. Thus, it was perhaps the most important movie ever made.
Roots had a larger audience share, though 46.0 is impressive.
“Thus, it was perhaps the most important movie ever made.”
I would add in “The China Syndrome” which did more to destroy nuclear power than the minor event at Three Mile Island, which happened less than two weeks after the movie came out.