THE FUNDAMENTAL CHANGES
The total units on the board have been roughly doubled. The cost of land units has been roughly doubled. The total income on the board has only been increased by only one third.

Land Units
Changes: New units that can be placed each round will represent a dramatically smaller fraction of the total forces. Players will have to use starting units more intelligently as heavy losses will be difficult to replace.

Furthermore, if a skilled player out-maneuvers a less skilled one, it will have a greater effect. For example, if Germany masses in the Ukraine they will likely draw Russian forces to Stalingrad. Germany can then capture West Russia, and be on Moscow’s doorstep. The Soviets will send everything they can to defend their capitol but, their infantry will not make it, and they will not be able to afford many new ones to place in Moscow, leaving their high value pieces vulnerable. With high value pieces harder to replace, this could spell total disaster for the Allies.

Historical Context: The game officially opens on June 1, 1942. At this point every country but the United States was fully mobilized. They continued to call up new recruits throughout the war, but these were barely enough to replace the casualties being suffered. Those casualties, in turn, represented a relatively small proportion of the forces in the field. On the rare occasion that a large force was lost, it was devastating. For example, the Wermarch never fully recovered from the loss of the Sixth Army at Stalingrad.

Naval Units
Changes: A loss of a major fleet is no longer more devastating than the loss of a major army. Players can afford to be more daring and take bigger risks with them.

The lower relative expense of naval units versus air units allows players to split their fleets more often. It is no longer worth sacrificing a fighter to take out an enemy's destroyer, meaning transports can be protected by a weak naval force, so long as it does not encounter an enemy fleet.

Historical Context: While the largest proportion of naval power remained in large task forces, convoys, usually escorted by a small number of cruisers and/or destroyers, were often formed to transfer/distribute resources as needed.