In 1915, he joined the army but suffered a breakdown and was indefinitely discharged. During the war, Morandi's still lifes became more reduced in their compositional elements and purer in form, revealing his admiration for both Cézanne and the Douanier Rousseau.
A Metaphysical painting (Pittura Metafisica) phase in Morandi's work lasted from 1918 to 1922. This was to be his last major stylistic shift; thereafter, he focused increasingly on subtle gradations of hue, tone, and objects arranged in a unifying atmospheric haze, establishing the direction his art was to take for the rest of his life. Morandi showed in the Novecento italiano exhibitions of 1926 and 1929, but was more specifically associated with the regionalist Strapaese group by the end of the decade, a fascist-influenced group emphasizing local cultural traditions. From 1930 to 1956, Morandi was a professor of etching at Accademia di Belle Arti. The 1948 Venice Biennale awarded him first prize for painting, he visited Paris for the first time in 1956, and in 1957 he won the grand prize in São Paulo's Biennale.
Throughout his career, Morandi concentrated almost exclusively on still lives and landscapes, except for a few self-portraits. With great sensitivity to tone, color, and compositional balance, he would depict the same familiar bottles and vases again and again in paintings notable for their simplicity of execution. Morandi executed 133 etchings, a significant body of work in its own right, and his drawings and watercolors often approach abstraction in their economy of means.
Morandi was one of the most impressive Italian painters of his day. Federico Fellini paid tribute to him in his film La dolce vita, which featured Morandi's paintings. Morandi was additionally perceived as one of the few Italian artists of his generation to have escaped the taint of Fascism, and to have evolved a style of pure pictorial values congenial to modernist abstraction. Through his simple and repetitive motifs and economical use of color, value and surface, Morandi became a prescient and important forerunner of Minimalism. He died in Bologna in 1964.