First of all there arent many US TRPGs Most seem to be made in Eastern Europe Secondly except for freeware games like Battle for Wesnoth and Galaxy Mage I dont see a lot of evidence of Western TRPGs being inspired by Japanese games When developers do mention their inspiration they tend to cite XCOM Jagged Alliance or Fallout The origin of XCOM dates back to Rebelstar and Laser Squad earlier games by the same developer that predate the Japanese TRPGs Thirdly it might be more accurate to say that both Eastern and Western TRPGs were partly inspired by the early Ultima games