Complex sentence: From 1919 to 1934, Squire was the editor of the important monthly periodical, the "London Mercury", a publication which showcased the work of the Georgian poets and was an important outlet for many new writers.
Split into simpler sentences: From 1919 to 1934, Squire was the editor of the monthly periodical, the "London Mercury". It showcased the work of the Georgian poets and was an important outlet for new writers.