From the very beginning, when Pakistan came into being in 1947. Pakistan is economically very week. Pakistan’s strategy is too built up friendly relationships with economically developed nations. So Pakistan try to strengthen relationship with USA, but initially America was not interested. However when communist revolution came in 1949, USA is compelled to make relationship with Pakistan. Pak US realationships are very important in 1950s, because Pakistan is included in American block, and Pakistan become a member of SEATO and CENTO.
After that due to some reasons President Ayub khan changes his foreign policy and chose the policy of bilateralism with two Super powers (USA and USSR). Because in the war against India in 1965 and in 1971,America did not help Pakistan, Even America stopped the selling of weapons. Due to this Pakistan beers a great loss .
But in 1979 America once again want to make friendly relationship with Pakistan, due to Islamic revolution in Iran and due to entrance of communist armies in Afghanistan. This is also an alarming situation for Pakistan. So,Pakistan accepted the proposal of America. However, now onward there are good relationships between Pakistan and America .