Complex sentence: The Soviet Union (which remembered the Ba'ath Party's anti-communist purge during its 1963 stint in power) gradually improved its relations with Iraq; in 1969, it guaranteed Iraq a sizable amount of modern arms and technical aid.
Split into simpler sentences: The Soviet Union, which still remembered the Ba'ath Party's anti-communist purge during their 1963 stint in power, improved their relations with Iraq gradually. In 1969, the Soviet Union guaranteed Iraq a sizable amount of modern arms and technical aid.