-(after the sentence.) Cassie and Ben have fulfilled their sacred mission of saving Sammy, the aliens' main military base has been blown to bits, and Cassie and the gang are headed off to relative safety.
the story ended because of the hard work or skill. cassie and Ben, other characters worked hard to save "humanity" or what's left.
Working hard irl is most important because that's how you can get things you want/need to succeed.
(I dont know if that answer is okay, but there?^)
