Why did the war become a turning point in Du Fu's life and a huge blank in his poetry?

Because Du Fu used to be the official family of the upper class, at that time, his poems mostly praised the beautiful life and prosperity, and the war broke all this.

Then the country fell into war, flood and famine. Du Fu's dream about Confucian ethics was shattered. From then on, Du Fu's poems began to show the historical image of China after the prosperous Tang Dynasty. During the eight-year turmoil, he experienced the displacement of his family and the disintegration of the country. Du Fu went down from the privileged class to the ordinary people and personally experienced the real picture of the bottom society.