Question

vietnam was divided at the 17th parallel into communist north and non-communist south vietnam.
the united states used the domino theory to justify its intervention in southeast asia.
the united states helped create , which was designed to be a military alliance to prevent the spread of communism.
nato
seato
the united nations

Explanation:

To solve this, we analyze each option:

• NATO (North Atlantic Treaty Organization) is a military alliance focused on Europe and North America, not Southeast Asia.
• SEATO (Southeast Asia Treaty Organization) was created with US help as a military alliance to prevent communism's spread in Southeast Asia, matching the context.
• The United Nations is a global organization for peace and cooperation, not a military alliance for this specific anti - communism purpose in Southeast Asia.

Answer:

B. SEATO