The Spartan is made in the Philipines by Armscor and then assemebled in the USA by STI with STI parts. The Ranger/Trojan are 100% made in USA.
The Spartans are actually manufactured in the "STI Section" of the Armscor plant in the Philippines. They are made with a cast frame and forged slide supplied by Armscor, but made to STI's specifications.
You are correct though that they are made with STI internal parts, supplied by STI to Armscor. The pistols are then given a QC inspection when they hit STI's warehouse/shop in Georgetown, TX before they are shipped out to the distributors.
Without a doubt, the Spartan is, hands down, the best value in a 1911. Period. There are cheaper 1911s that are good and there are more expensive 1911s that are better... But there is no other 1911 that give you the bang for your buck that the STI Spartan gives you.
As already mentioned, the Trojan/Ranger series are made entirely by STI in their shop in Georgetown, TX. They use a cast frame, featuring "STIppled" front strap and high cut trigger guard. The slides used on the Trojan and Ronger series are forged.
The Rangers are commander length guns and use a bushingless bull barrel and STI's RecoilMaster guide rod. Rangers come with fixed Heinie sights. The Trojans are full length (government length) pistols and come with a bushing barrel and standard full length guide rod. Adjustable sights are standard on the Trojans, but fixed sights are a factory order option.