Complex sentence: The river port at the junction of the Grand Canal served as both an inland port and seaport supplying the Northeast border of various Chinese states, and since 1153, it was the critical supply hub for what is now Beijing.
Split into simpler sentences: The river port at the junction of the Grand Canal served as both an inland port and seaport supplying the northeast border of Chinese states. Since 1153, it was the critical supply hub for what is now Beijing.