Complex sentence: Other schools soon applied for affiliation with the Pershing Rifles, and by the middle of the 20th century this now national organization comprised nearly 200 units representing all of the services stationed at ROTC detachments around the country.
Split into simpler sentences: Other schools soon applied for affiliation with the Pershing Rifles. By the middle of the 20th century, this now national organization comprised nearly 200 units representing all of the services stationed at ROTC detachments around the country.