Which military alliance was formed to deter Soviet aggression during the Cold War?

The North Atlantic Treaty Organization (NATO) was established in 1949 as a collective defense alliance among Western nations, specifically to deter Soviet aggression during the Cold War. Its formation was a response to the increasing tensions and threats from the Soviet Union in Europe. NATO's central principle is mutual defense, meaning that an attack against one member is considered an attack against all members, which was intended to create a unified front against potential Soviet expansion.

NATO played a crucial role in maintaining stability in Europe during the Cold War by providing military assurance to its members, thus contributing to the deterrence strategy against the Soviet bloc. The collaboration among member countries facilitated military coordination and strategic planning, which was vital in the context of the division of Europe into East and West.

The other alliances mentioned, like the Warsaw Pact, were established later but served a different purpose as a response to NATO, while others like the League of Nations predate the Cold War and lacked the military commitment necessary for the context of deterrence. SEATO, while relevant to Cold War strategies in Asia, did not encompass the broader European focus of the primary Cold War tensions, making NATO the correct primary alliance for this purpose.