Question

Is this a run-on sentence?

Answer 1

Yes. You can separate the sentence at “Nearly two years later...” by adding a period after CIA.

Answer 2

Yes, this is a run-on sentence.

There are many commas, but only one period at the end.  There are also many spots where there were opportunities to add another period (to make it a normal sentence).

Here is a revised version:

"In 1960, American pilot Francis Gary Powers was shot down and captured by the Soviets.  This occurred as he flew over the Ural Mountains on an intelligence mission for the CIA. Nearly two  years later, Powers was released in exchange for Rudolf Abel, a KGB spy who had been  caught in the United States."

I hope this helps!

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