Complex sentence: Political relations became strained under the rule of Mahathir bin Mohamad, who ruled from 1981 until 2003, and who was very critical of the foreign policy of the United States.
Split into simpler sentences: Political relations became strained under the rule of Mahathir bin Mohamad. Tun Dr. Mahathir ruled from 1981 until 2003 and was critical of the foreign policy of the United States.