National Characteristics?

[Blackcloud6]

In my thread on taking towns and entrenchments Peter said with Americans you use firepower and that is a national characteristic of the American Army in WWII.  It was a firepower army so cool, PG replicates that.  

To me at times, the various armies in PG can appear to be somewhat generic.  So what are the nuances that make the armies different in PG and what are their effects?  How should the armies be played?  What are their strengths and weaknesses?