Complex sentence: French construction of defensive lines and the arrival of reinforcements before the opening attack, were able to delay the German advance despite many losses and by 6 March divisions were in the RFV and a defence in depth had been established.
Split into simpler sentences: French construction of defensive lines and the arrival of reinforcements before the opening attack, were able to delay the German advance despite many losses. By 6 March divisions were in the RFV and defence in depth had been established.