Complex sentence: Each of the Masters' previous androids had a lifespan of several hundred years, assembling its replacement, but the unexpected, rapid advent of nuclear physics and the radioactive fallout from above-ground nuclear testing now present within the environment had damaged Vaslovik.
Split into simpler sentences: Each of the Masters' previous androids had a lifespan of several hundred years, at the end of which each assembled its replacement. The unexpected, rapid advent of nuclear physics and the radioactive fallout from above-ground nuclear testing had damaged Vaslovik.