The US membership in SEATO showed Amercais commitment to stopping the spread of communism on a global scale.
After World War II ended, the US and Soviet Union emerged as global superpowers. These two vastly different nations used two different economic/political systems to run their country. Americans feared that the system of communism, used by the Soviet Union, would continue to spread to other countries at this time. This is why the US government adopted the policy of containment. This policy was focused on stopping the spread of communism on a global scale. This helps us to understand why the US join this organization. Along with this, it helps us to understand why the US joined both the Korean and Vietnam Wars.