Everyone into the pool!

[CrusssDaddy]

My experience with neutrals: less is more. Bring in Spain, Turkey, Sweden to whichever side is most interesting (usually Axis for the first two and Allies for the latter). Having Mexico and Brazil+Argentina be Axis can also be interesting for a couple early turns. But my initial games were treated like Risk and I was drafting all the neutrals, which can become very tedious with lots of low intensity wars that linger pointlessly or cakewalks that lack drama.

[Extraneous]

If you really want to mess up Axis production make all neutrals aligned to the axis.

Imagine what it does to the force pool when all the neutrals are added to them.

[Centuur]

The Axis don't have to include all those units to their forcepool if they don't want too...

RAW:

After a minor country has aligned with you, you can choose to add its
units (those not yet set-up) to your major power’s force pools. You
can do this at any time while the minor is not conquered (incomplete
or complete) but, once you do, its units must always go into your force
pools as they become available.

[Extraneous]

True, but until they are added to the Force pools they cannot be purchased with BP and added to the game as reinforcement.