Complex sentence: The simulation ends, and Ender believes the test is over, but the commanders restart the video screens, showing that the destruction of the Formic homeworld was real and Ender had been controlling the real fleet this time.
Split into simpler sentences: The simulation ends, and Ender believes the test is over. Then the commanders restart the video screens, showing that the destruction of the Formic homeworld was real and Ender had been controlling the real fleet this time.