Complex sentence: Tankettes were designed and built by several states between the 1920s and 1940s, and saw some combat (with limited success) in World War II. However, the vulnerability of their light armor eventually caused the concept to be abandoned.
Split into simpler sentences: Tankettes were designed and built by several nations between the 1920s and 1940s. Some saw some combat (with limited success) in World War II. However, the vulnerability of their light armor eventually caused the concept to be abandoned.