Complex sentence: It was once the world's flour milling capital and a hub for timber, and today is the primary business center between Chicago and Seattle, with Minneapolis proper containing America's fifth-highest concentration of Fortune 500 companies.
Split into simpler sentences: It was once the world's flour milling capital and a hub for timber. In the 21st century, it is the primary business center between Chicago and Seattle, with Minneapolis proper containing America's fifth-highest concentration of Fortune 500 companies.