One month later, the proposed European Treaty was rejected not only by supporters of the EDC but also by western opponents of the European Defense Community (like French Gaullist leader Palewski) who perceived it as "unacceptable in its present form because it excludes the USA from participation in the collective security system in Europe". The Soviets then decided to make a new proposal to the governments of the USA, UK and France stating to accept the participation of the USA in the proposed General European Agreement. And considering that another argument deployed against the Soviet proposal was that it was perceived by western powers as "directed against the North Atlantic Pact and its liquidation", the Soviets decided to declare their "readiness to examine jointly with other interested parties the question of the participation of the USSR in the North Atlantic bloc", specifying that "the admittance of the USA into the General European Agreement should not be conditional on the three western powers agreeing to the USSR joining the North Atlantic Pact".
The omission of which nation from involvement in the proposed security system led to its NATO opposition?
the USA