What was the first 2D animated movie?

The first 2D animated movie is generally considered to be "Snow White and the Seven Dwarfs", released by Walt Disney Productions in 1937.

While other animated films existed before, such as "The Adventures of Prince Achmed" (1926) and "Steamboat Willie" (1928), "Snow White" was the first full-length animated feature film, and its success helped to establish animation as a legitimate form of entertainment.