Didn't we also need to shed light on the reasons and [B]trends[B] which led to the expansion of the powers of the federal government instead of just detailing the different theories held regarding the functioning of the federal government?

An alternative approach could have been to explain the various causes that gave birth to the rise of federal government's strength. For instance, the failure of Articles of Union convinced the newly independent colonists to form a strong central government. Similarly, the federating units were not appropriating the requisite money to the central government and often, the troops were just issued a certificate, which could be redeemed later.

Treading along, the Civil War events could account for the further rise in the expansion of the federal government's power. The Union had to be preserved and the North's victory meant that a Union was the ultimately reality - and no state could challenge it. This belief ultimately paved the way for the incontrovertible power of the federal government. The issue was settled once for all.

The post Civil War trends include the emergence of the construction of inter-state rail roads, inter-state rail commerce and the various disputes between the states, where the federal government inevitably had to play an effective mediating role. Its power continued to rise.

Best of luck to all the aspirants.