make common cause with

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