Complex sentence: He campaigned for Britain to relinquish its colonial rule, which Britain did in 1963, when Singapore merged with Malaya, Sabah and Sarawak to form the new federation of Malaysia.
Split into simpler sentences: He campaigned for Britain to relinquish its colonial rule. Britain withdrew in 1963, when Singapore merged with Malaya, Sabah and Sarawak to form the new federation of Malaysia.