Numerous Midrashim list different things that the world was created for the purpose of such as Klal Yisrael, Bikkurim, Torah, Challah, and Maasros all of which are called "ראשית" (first).
I remember seeing somewhere (along with a very nice Vort for it) that one of the things the world was created for was Amalek because Amalek is called Reishis in Bamidbar 24:20
במדבר כד:כ - וירא את עמלק וישא משלו ויאמר ראשית גוים עמלק ואחריתו עדי אבד:
Does anyone know what the source for this is? Thanks.