And it had to do with we attacking Kiri with you guys coming to their rescue breaking the "gentleman's agreement" we had before.
That and well, you guys are the least prone village to arguments.
Kiri is a headache to fight against. Suna is not far from it. Iwa has good relations to us. Ame and Akatsuki are allied with us. So a War with kumo was bound to be more enjoyable for both sides than a war with any other country. Thus why we chose you.
That and we hate clouds. Whats you gonna do? lol