Promote a sense of membership
Belonging also comes from the benefits that people gain, so work on the reward and recognition system. Help people manage their careers, making promotions meaningful and not being promoted acceptable.
More than anything else, the most important process in an organization is selection, whether it is promotion or recruitment from outside. Creating a meritocracy means this is done fairly, with a focus on the best person for the job rather than on favoritism.
When people join, have a very deliberate process of socialization, where they learn the culture and the present organization. Having senior managers present to the new recruits sends a very powerful message. Likewise in training and development, a consistent promotion of the culture through all things sustains the message and the meaning.
Socialization often starts with a humility-inducing experience that shows the person that they really do not understand how things work. This is followed by an in-the-trenches immersion that inculcates the culture.