Pakistan aligned with the U.S. to counter India's regional dominance. [causal]
Pakistani domestic and foreign policies have from the start been shaped by a felt need for parity with neighboring India. Specific disagreements with India, such as the dispute about the fate of Kashmir after independence, led Pakistan to search for international relationships that would aid its own security. In the early years after the Second World War, Pakistani anxieties met with the U.S. desire for client states in South and Southeast Asia to combat the regional threat from the Soviet Union. … Thus, Pakistan became an important player in the international anti-Communist alliance of the 1950s and 1960s: a position that—rather ironically for a new nation—set it against that popular anti-imperial sentiment widespread during the period as decolonization and anticolonial nationalist crises in Iraq, Egypt, the Republic of Congo, and Indochina drew popular support across the Third World.
Peter Morey, Islamophobia and the Novel, loc. 385