Esprit de corps

a sense of unity and of common interests and responsibilities, as developed among a group of persons closely associated in a task, cause, enterprise, etc.

Still the Senator was tranquil, for he knew that there is an esprit de corps in the Senate which does not exist in the House, the result of which is to make the members complaisant towards the projects of each other …
Mark Twain and Charles Dudley Warner, The Gilded Age, 1873

The pay was atrocious, the facilities were run-down, and the duty was often grueling. What made it all bearable was the esprit de corps, the brotherhood, and the pride that went along with training at such a high level.
Vince Flynn, Consent to Kill, 2005

Esprit de corps was borrowed into English from French around the 1770s.