In the movie, the human race really tried so hard so that they can win the war but in the final moment, Riku finally summon the Star Cup but unfortunately his both arm were blast off... and then Tet finally show up and give a hand to Riku.
After that, Tet use his power to repair the whole world and made the world calm down for awhile. So basically it was Tet power that made the world peace for awhile but isn't the human race actually contribute more than Tet right?
If Riku didn't plan this, Tet wouldn't come out and help the human race right?