(S (S (BASENP (DT This)) (VP (VBZ is) (VP (ADVP (RB mainly)) (VP (VBN used) (PP (IN by) (NP (BASENP (JJ American) (NNS troops)) (SBAR (WHNP (WDT which)) (S (VP (VBP train) (BASENP (JJ Afghan) (NN security) (NNS forces))))))))))) (PERIOD .))