Complex sentence: In 1901, after extensive study of sociological and architectural problems, he began to formulate an elaborate solution to the perceived issues concerning urban design and published his major treatise "Une cité industrielle" in 1918.
Split into simpler sentences: In 1901, after extensive study of sociological and architectural problems, he began to formulate an elaborate solution to the perceived issues concerning urban design. Garnier published his major treatise "Une cité industrielle" in 1918.