Complex sentence: By 1820 Zahlé's population had grown to 5,000 and by 1850 it was 7-8,000 and it had become the commercial centre for the Beka'a and main depot for the local grain harvest.
Split into simpler sentences: By 1820 Zahlé's population had grown to 5,000. By 1850 it was 7-8,000 and the town had become the commercial centre for the Beka'a and main depot for the local grain harvest.