[quote=Rare]
Why does Mexico have those land or either one. It's close to them and they can keep a eye on it.
[/quote]
Conceivably, Britain could sell Belize to Mexico, sure. The point of all this is that Mexico [i]does[/i] stand to benefit from entering this war. Take out some Dutch colonies in exchange for better relations and maybe some territorial gains plus that whole debt thing.

Staying neutral yields nothing.

Joining the Coalition makes an enemy out of the side that currently controls the seaways.

Of the three options, the former makes the most sense.