Assertion: India signed a 20-year Treaty of Peace and Friendship with the Soviet Union in August 1971.
Reason: Henry Kissinger, the adviser to US President Richard Nixon, made a secret visit to China via Pakistan in July 1971.

Both the Assertion and the Reason are correct and the Reason is the correct explanation of the Assertion.

The US-China rapprochement that began in the late 1960s resulted in a realignment of forces in Asia. Henry Kissinger, the adviser to the US President Richard Nixon, made a secret visit to China via Pakistan in July 1971. In order to counter the US-Pakistan-China axis, India signed a 20-year Treaty of Peace and Friendship with the Soviet Union in August 1971. This treaty assured India of Soviet support if the country faced any attack.