Ayub Khan's presidency allied Pakistan with the American-led military alliance against the Soviet Union which helped Pakistan developed its strong economic background, long-term political and strategic relations with the United States. Major economic aid and trade from the United States and European Communities ultimately led Pakistan's industrial sector developed rapidly but the consequences of cartelization included increased inequality in the distribution of wealth. After 1965, he became extremely concerned about the arrogance and bossiness of the US over the directions of nation's foreign policy when the US publicly criticized Pakistan for building ties with China and Soviet Union; he authored a book over this issue known as "Friends not Masters".