Complex sentence: Despite the initial enthusiasm, the Atomic Gardening Society declined by the mid 1960s, in combination with a shifting political climate away from atomic energy and a failure on the part of the crowd sourced Society to produce noteworthy results.
Split into simpler sentences: Despite the initial enthusiasm, the Atomic Gardening Society declined by the mid 1960s. This was due to a combination of a shifting political climate away from atomic energy and a failure on the part of the crowd sourced Society to produce noteworthy results.