Throughout Henry IV Part 1 we're reminded that civil war is a family affair, one that threatens to tear apart the collective kingdom. The play begins and ends with portrayals of warfare and promises that civil strife will continue in the sequel, Henry IV Part 2. In the play, war is largely associated with masculinity and honor. For Prince Hal especially, the battlefield is a place for redemption and transformation. While several members of the nobility attempt to elevate the physical horrors of war to something lofty and noble, the play also gives voice (via Falstaff) to the idea that the violence of warfare is meaningless and hollow.
In Henry IV Part 1 warfare is an exclusively masculine realm with no room for women or effeminacy.
In Shakespeare's play, warfare is portrayed as a family affair in order to demonstrate the unnaturalness of civil war.