USA and Soviet Union

The Soviet Union sympathized with the East Pakistanis, and supported the Indian Army and Mukti Bahini's incursion against Pakistan during the war, in a broader view of recognizing that the succession of East Pakistan as Independent Bangladesh would weaken the position of its rivals— the United States and China. The Soviet Union gave assurances to India that if a confrontation with the United States or China developed, it would take counter-measures. This assurance was enshrined in the Indo-Soviet Treaty of Friendship and Cooperation signed in August 1971.

However, the Indo-Soviet treaty did not mean a total commitment to every Indian position, even though the Soviet Union had accepted the Indian position during the conflict, according to author Robert Jackson. The Soviet Union continued its sympathetic gesture to Pakistan until mid-October 1971, when it stressed Pakistan to come up with a political settlement and affirmed its continuation of industrial aid to Pakistan. By November 1971, the Soviet ambassador to Pakistan Alexei Rodionov directed a secretive message (Rodionov message) that ultimately warned Pakistan that "it will be embarking on a suicidal course if it escalates tensions in the subcontinent.

The United States stood with Pakistan by supporting it morally, politically, economically and materially when U.S. President Richard Nixon and his Secretary of State Henry Kissinger refused to use rhetoric in a hopeless attempt to intervene in a large civil war. The U.S. establishment perceived to the impression that they needed Pakistan to help stop Soviet influence in South Asia in an informal alliance with India. During the Cold War, Pakistan was a close formal ally of the United States and also had close relations with the People's Republic of China, with whom Nixon had been negotiating a rapprochement and where he intended to visit in February 1972.Nixon feared that an Indian invasion of Pakistan would mean total Soviet domination of the region, and that it would seriously undermine the global position of the United States and the regional position of America's new tactical ally, China. Nixon encouraged Jordan and Iran to send military supplies to Pakistan, while also encouraging China to increase its arms supplies to Pakistan, but all supplies were very limited. The Nixon administration also ignored reports it received of the "genocidal" activities of the Pakistani military in East Pakistan, most notably the Blood telegram, and this prompted widespread criticism and condemnation – both by the United States Congress and in the international press.

Then U.S. Ambassador to the United Nations, George H.W. Bush, introduced a resolution in the UN Security Council calling for a cease-fire and the withdrawal of armed forces by India and Pakistan.^[However, it was vetoed by the Soviet Union, and the following days witnessed the use of great pressure on the Soviets from the Nixon-Kissinger duo to get India to withdraw, but to no avail.

When Pakistan's defeat in the eastern sector seemed certain, Nixon deployed Task Force 74, led by the aircraft carrier USS Enterprise, into the Bay of Bengal. Enterprise and its escort ships arrived on station on 11 December 1971.According to a Russian documentary, the United Kingdom also deployed a carrier battle group led by the aircraft carrier HMS Eagle to the Bay, on her final deployment.

On 6 and 13 December, the Soviet Navy dispatched two groups of cruisers and destroyers from Vladivostok; they trailed US Task Force 74 into the Indian Ocean from 18 December 1971 until 7 January 1972. The Soviets also had a nuclear submarine to help ward off the threat posed by the USS Enterprise task force in the Indian Ocean.

As the war progressed, it became apparent to the United States that India was going to invade and disintegrate Pakistan in a matter of weeks, therefore President Nixon spoke with the USSR General Secretary Leonid Brezhnev on a hotline on 10 December, where Nixon reportedly urged Brezhnev to restrain India as he quoted: "in the strongest possible terms to restrain India with which … you [Brezhnev] have great influence and for whose actions you must share responsibility."

After the war, the United States accepted the new balance of power and recognized India as a dominant player in South Asia; the US immediately engaged in strengthening bilateral relations between the two countries in the successive years. The Soviet Union, while being sympathetic to Pakistan's loss, decided to engage with Pakistan after sending an invitation through Rodionov to Zulfikar Ali Bhutto, who paid a state visit to the Soviet Union in 1972 to strengthen bilateral relations that continued over the years.

A 2019 study argues "that Nixon and Kissinger routinely demonstrated psychological biases that led them to overestimate the likelihood of West Pakistani victory" in the war, and that they overestimated "the importance of the crisis to broader U.S. policy. The evidence fails to support Nixon and Kissinger's own framing of the 1971 crisis as a contest between cool-headed realpolitik and idealistic humanitarianism, and instead shows that Kissinger and Nixon's policy decisions harmed their stated goals because of repeated decision-making errors.