Complex sentence: This line was at first built for the Sultan, but later served the heavy population along the northeastern shores of the Sea of Marmara, but few trains ran on the line during the time the government operated it.
Split into simpler sentences: This line was at first built for the Sultan, but later served the heavy population along the northeastern shores of the Sea of Marmara. However, few trains ran on the line during the time when the government operated it.