Complex sentence: Control of the economy, of citizens and of colonial policy were only cosmetically relaxed before the left-wing Carnation Revolution in 1974, which led to attempts to introduce democratic socialism and eventually allowed for the restoration of a full parliamentary democracy.
Split into simpler sentences: Control of the economy, of citizens and of colonial policy were only cosmetically relaxed until the left-wing Carnation Revolution in 1974. The latter led to attempts to introduce democratic socialism and eventually allowed for the restoration of a full parliamentary democracy.