The Iran–Iraq War is also noted for Iraq's use of chemical weapons and biological weapons against Iranian troops and civilians. The role of the United States and Soviet Union was very important, dating back to the Cold War. In 1953, the US encouraged a coup d'état against Mohammad Mosaddegh, who was the Prime Minister of Iran. Shah Mohammad Reza Pahlavi returned to power, supporting his military and his government. The United States sold many weapons to the Shah's government. Meanwhile, revolutionaries of the Arab Socialist Ba'ath Party overthrew the king of Iraq and, with the help of the Soviet Union, built up their army. Starting with the United Arab Republic, they sought to unite all the Arabs into one state, including the Arab minority in Iran.