The Quadrilateral Security Dialogue, commonly known as QUAD, is an informal strategic forum aimed at promoting security dialogue and cooperation, particularly to address China's growing economic and military influence. It consists of four key countries:
- United States of America (U.S.A.)
- Japan
- Australia
- India
These nations collaborate on various aspects, including military cooperation, economic partnerships, and strategic discussions to ensure a free and open Indo-Pacific region. Thus, the correct answer for the countries involved in QUAD is: U. S. A., Japan, Australia and India.