What constitutes a nuclear threat? This study uses the following definition:
1. Observable actions taken, such as increasing nuclear alert levels, the flight-testing of nuclear-capable missiles, or the repositioning of significant military forces capable of employing nuclear weapons to demonstrate resolve during a crisis or in warfare.
2. Statements (whether made in public or transmitted through private channels and subsequently disclosed) by high-ranking government officials or their representatives during a crisis or in warfare expressing or indicating a willingness to use nuclear weapons in defense of national interests.