Complex sentence: The tier system refers to Special Operations Forces capabilities within the United States Armed Forces and can also be applied to special forces counterparts in other nations who may or may not have the same skill set/skill level, but who do occupy the same niche.
Split into simpler sentences: The tier system refers to Special Operations Forces capabilities within the United States Armed Forces. The Tier association is sometimes applied to Special Operation counterparts in other nations who may or may not have the same skill set/skill level, but who do occupy within the same niche.