The key element in creating a space of Belonging is: Respect.
Respecting who each team member is, what they can offer, how they can contribute and why they've chosen to work on this important cause. Leadership sets the tone with decisive, visible actions, both in terms of organizational policies and processes as well as clear leadership role modeling of things such as participative decision-making and advocacy for underrepresented groups.
Social connection is a really large part of this. Belonging itself can also directly impact trust on teams. This article by Fast company is an interesting read on how social connection impacts this.
Belonging is the sweet spot where Inclusion, Diversity and Equity overlap. (see Venn diagram below)