Complex sentence: The Garment District has been known since the early 20th century as the center for fashion manufacturing and fashion design in the United States, and even the world; no other city has a comparable concentration of fashion businesses and talent in a single district.
Split into simpler sentences: The Garment District has been known since the early 20th century as the center for fashion manufacturing and fashion design in the world; no other city has a higher concentration of fashion businesses and talent in a single area. No other city has a comparable concentration of fashion businesses and talent in a single district.