There is no universally accepted definition of a mountain. Elevation, volume, relief, steepness, spacing and continuity have been used as criteria for defining a mountain. In the Oxford English Dictionary a mountain is defined as "a natural elevation of the earth surface rising more or less abruptly from the surrounding level and attaining an altitude which, relatively to the adjacent elevation, is impressive or notable."So, which are the largest countries without a "mountain?" Ponder your answer before peeking below the fold. The one I guessed came out #5 on their list.
9. The Gambia
At the source, comments suggest that Uruguay and the Netherlands were overlooked.