What agreement does Capulet make with Paris?

From the very beginning of the play, Paris is introduced as a potential suitor for Juliet, and Capulet seems to look upon the arrangement favourably. He does, however, request that Paris wait two years, as he believes Juliet is still too young to be married.

However, after Tybalt has been slain and Romeo banished, Capulet changes his tone:

CAPULET
Sir Paris, I will make a desperate tender
Of my child's love: I think she will be ruled
in all respects by me; nay, more, I doubt it not.
(Act III, Scene 4)

At which point, he agrees that Juliet and Paris will be married "Thursday next", today being Monday.

What is the reason for his sudden change of heart? He isn't yet aware of Juliet's love for Romeo at this point, so perhaps he simply thinks that the best cure for unhappy events (Tybalt's death) is a happy one (a wedding party). Also, if the Capulet/Montague feud is escalating, then it would be in his best interest to gain Paris as an ally, and to ensure Juliet is married before any other calamity strikes the family.