make common cause with
US /meɪk ˌkɑː.mən ˈkɑːz wɪθ/
UK /meɪk ˌkɑː.mən ˈkɑːz wɪθ/

1.
to join with someone else in order to achieve a shared aim
:
•
The two rival factions decided to make common cause with each other against the invading army.
•
Environmental groups often make common cause with local communities to protect natural habitats.