Explanation

The three countries that have not signed the CTBT are:

• India
• North Korea
• Pakistan

These countries are also among the eight Annex 2 states that have not ratified the treaty.

 The United States was the first nation to sign the treaty.

Signatories:187

Ratifiers: 178

Additional information 

CTBT stands for Comprehensive Nuclear-Test-Ban Treaty 

It's a multilateral treaty to ban nuclear weapons test explosions for both civilian and military purposes

Signed: 24 September 1996

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