Since I've just been immersed in the first Henry VI play, background info seems a little less necessary for the next one. Nevertheless, the preface I just finished reading was fascinating (Tony Tanner's Prefaces to Shakespeare). Evidently, this play holds together a bit better than the first and is a little more historically accurate. Shakespeare still compresses history and adapts a few things to fit his theme but it sounds like a great read.
As Tanner writes, "In the first part of the trilogy, England lost its old heroes. In this second part, it loses (in the symbolic form of one man) its law-givers." The new queen, Margaret of Anjou, Suffolk, and Cardinal Winchester plot against Gloucester, the Lord Protector. His wife is accused of witchcraft and imprisoned and he is eventually murdered, though historians doubt the latter. All these complicated plans backfire, however, and leave the kingdom open for Richard, Duke of York (father of Edward IV and Richard III) to claim the crown and begin the War of the Roses. The play depicts the fall of a leader and the descent of the nation into mayhem with riots, pirate attacks, and battle.
Interestingly, one of my historical sources pointed out that the War of the Roses would not have been severely felt by most of the common people. There were only two major battles and the skirmishes may have had negative affects on the towns and fields nearby but the whole nation was not embroiled by the conflict and most of the deaths were of the nobility. Now what that meant for the government at large is a different matter, perhaps why Shakespeare is so interested in displaying the dangers of civil war.
I will be interested to see how the Yorkists become "evil" as the play progresses. Richard, Duke of York didn't seem especially villainous--I was cheering for him to re-attain his family's title in part I. Also, young Richard III appears, already with hints of malice, though in most scenes he either would have been elsewhere, imprisoned with his mother, or would have been too young to be present.