Explanation:

Under Article 352 (National Emergency), the President can declare a national emergency when the security of India or a part of it is threatened by war or external aggression or armed rebellion. It may be noted that the president can declare a national emergency even before the actual occurrence of war or external aggression or armed rebellion, if he is satisfied that there is an imminent danger.
Originally, the Constitution mentioned ‘internal disturbance’ as the third ground for the proclamation of a National Emergency, but the expression was too vague and had a wider connotation. Hence, the 44th Amendment Act of 1978 substituted the words ‘armed rebellion’ for ‘internal disturbance’. Thus, it is no longer possible to declare a National Emergency on the ground of ‘internal disturbance’ as was done in 1975 by the Congress government headed by Indira Gandhi.
The President, however, can proclaim a national emergency only after receiving a written recommendation from the cabinet. This means that the emergency can be declared only on the concurrence of the cabinet and not merely on the advice of the prime minister. In 1975, the then Prime Minister, Indira Gandhi advised the president to proclaim emergency without consulting her cabinet.