I spelled out FID a couple of posts earlier
Foreign Internal Defense
In lay terms - sending guys into a country to train host nationals how to fight against an insurgency
Unconventional Warfare is similar, but has layers of difference - sending guys into a country to train host nationals (and potentially others) to become an insurgency
As an example… late 2001… 5th Special Forces sent teams covertly into Afghanistan to arm, train, and help lead the Northern Alliance against the Taliban government. They were there before conventional troops arrived, operating alone, etc… the movie “12 Strong” is about one of those teams… this is UW…
By 2002 the US had displaced the Taliban and installed the Karzai government… Afghanistan needed a military and police force to secure the country against insurgents, remnants of the Taliban, and jihadists coming in from abroad… so Special Forces transitioned teams to FID… and started teaching Afghans essentially how to be an army..
Army Special Forces (Green Berets) are the primary force the US uses for these two missions, although other SOF units have some capability to do them as well. This is because FID and UW are core mission sets for SF where they are largely seen as ancillary for SEALs, MARSOC, etc.. and SF units are responsible for specific regions of the world where MARSOC is a global force… so for example, 10th Group is assigned to Europe as its area of operations.. so guys assigned to 10th Group will learn European languages (mostly Russian, German, etc) and will study European culture, religion, common courtesies and customs, etc and will get regularly stationed in Europe during their careers… 7th Group is Latin America.. so those guys learn Spanish and Portuguese and a few other languages spoken in the Caribbean, etc.. they study Latin American cultures, religion, customs, etc… 3rd gets Africa, 5th gets the Middle East, North Africa, and some of SW Asia… 1st gets Asia-Pacific… then 19th and 20th (National Guard Special Forces)are broken up and aligned with the different active duty groups)..
While some MARSOC or SEAL or USAF SOF might know foreign languages or have some cultural training, etc.. it’s not commonplace.. for SF it’s mandatory.. which puts FID and UW right in the SF wheelhouse…and something of an extra task for the others…