Complex sentence: At the time of its independence in 1960, the Democratic Republic of the Congo was the second most industrialized country in Africa after South Africa; it boasted a thriving mining sector and its agriculture sector was relatively productive.
Split into simpler sentences: At the time of its independence in 1960, the Democratic Republic of the Congo was the second most industrialized country in Africa after South Africa. It boasted a thriving mining sector and its agriculture sector was relatively productive.