The remarkable similarities between Oz and Middle-Earth
The first film version of L. Frank Baum's The Wizard of Oz was released in the summer of 1939, less than a month before World War II officially began. Though started as early as 1937, The Lord of the Rings was largely composed during the war years, but not published until somewhat later.
Therefore, it is by no means impossible that J.R.R. Tolkien saw the magnificent MGM movie before he wrote most of his magnum opus. Could Oz have influenced his tale somehow, consciously or unconsciously?
Well, people are influenced by everything they encounter, but Tolkein constructed the core of the Middle Earth mythos, stories and background during his service in World War I. The Two Towers extended DVD collection has a lot to say about his world and influences.
If he were influenced by Oz, I'd expect it would be the books much more than the movies.
Yes, as the page states, the similarities are more due to storytelling structure and archetypes than to any inherent influence.
Much of Tolkien is influenced by Welsh and Germanic legends.