They were people already struggle with the Titans for a long time and had seen the last titan hundred years ago . Now that a hundred years later , they decided to attack the Titans again humanity. The Titans are determined monsters to destroy the human race . Humanity had built a great wall to protect them from monsters . Titans almost succeeds in destroying the wall. Few people remained vulnerable under the defense was feared . The fate of the human species could be the last for mankind liberation struggle to be waged primarily Eren .