They were both developed in reaction to World War I.
Explanation:
While Dadaism which started around 1913, is a movement in which some artists rejected the logic, reason, and aestheticism of modern capitalist society, by displaying nonsense, irrationality, and anti-bourgeois protest in their works, and at the same time maintained political interest with the radical left.
Surrealism, on the other hand, was popular between 1920s and 1930s, and tried to access the subconsciousness of people and then translate this flow of thought into form of art.
Hence, Dadaism and Surrealism were both developed in reaction to World War I.
