What are some contrasts between love and war in Act 1 of Much Ado About Nothing?
The most obvious contrast that comes to my mind is Claudio and his attentions to Hero as he explains to Don Pedro in Act I scene 1. There is a definite distinction made between the time of war, when thoughts of love are not possible and, indeed, can be a distraction, and the time of peace, where thoughts of love can be entertained and focused upon. Note what he says to Don Pedro towards the end of this scene:
When you went onward on this ended action
I look'd upon her with a soldier's eye,
That lik'd, but had a rougher task in hand
Than to drive linking to the name of love.
But now I am return'd, and that war-thoughts
Have left their places vacant, in their rooms
Come thronging soft and delicate desires,
All prompting me how fair young Hero is,
Saying I lik'd her ere I went to wars.
Note how Claudio before war was able to "like" Hero, but because he had a "rougher task in hand," liking was not allowed to become love. However, now that "war-thoughts / Have left their places vacant," war has allowed space and time to entertain that "liking" might actually be "loving," and thus Claudio is entertaining marriage with Hero.