Did Walt Disney invent animation?

In short, no. Although he did patent an invention which would change the face of the industry - arguably more so than any other in the thousand years before its advent.

Early Animation

Animation has been around for thousands of years, in the form of flip books or other mechanisms that spin a reel (or drum) of sequential images to produce the illusion of movement. The earliest solid example of either type comes from a Zoetrope-type device traced back to China in the 2nd Century AD. Animation as projected from a film has itself been around since the late 1800s.

Disney Gets His Start...

Walt Disney got his start using common animation techniques available in the early 1900s - including the pioneering use of Cinephone (sound-on-film) process to create the famous Steamboat Willie cartoon of 1928.

...Then Sparks a Revolution

Then, in 1936, Walt Disney patented the Art of Animation - using the Multiplane Camera in a way that allowed animators to reuse backgrounds and other unchanged portions of an animated film. Not only did this drastically cut the time needed to produce and animate the movie itself, it also helped improve the overall quality of the completed film. This method also helped create the illusion of depth as some portions of the scene would appear to move faster than others (or stand still, in some cases).

A year later, Disney released "Snow White and the Seven Dwarfs," not only the first feature-length animated film, but also the first to take full advantage of the Multiplane Camera. Indeed, the film may never have been such a success without this invention.

Disney may not have "invented animation," but his techniques and the pioneering use Multiplane Camera certainly boosted the art into the mainstream. The technique would be used widely by Disney and other animators alike for another 50 years until the rise of computer animation in the 80s and 90s prompted its decline.