Complex sentence: Out of a population of 600,000, an estimated 200,000 Greek-Cypriots had been uprooted and forced to flee south of the Attila line, while an estimated 60,000 Turkish-Cypriots remained south of the Attila line, uncertain of their fate.
Split into simpler sentences: Out of a population of 600,000, an estimated 200,000 Greek-Cypriots had been displaced and fled south of the Attila line. At the same time, an estimated 60,000 Turkish-Cypriots remained south of the Attila line, uncertain of their fate.