make common cause with (someone or something)
To work together to do or accomplish something. We've made common cause with the surrounding neighborhoods to stop the city from paving over the local baseball fields.
make common cause with
unite with in order to achieve a shared aim. 1997 A. Sivanandan When Memory Dies I was sorry that the crows, proud kings of the dung-heap, should make common cause with house-sparrows under the eaves of roofs.