A bone fusion device can include elongated interlockable segments, each having an engaging surface interlockable with the engaging surface of another segment. The segments can be inserted in between bones one at a time. A device can include an outer expandable component having outer expandable members insertable to a location between bones in an unexpanded configuration and an inner expander including surface engaging portions interlockable with inner surface engaging portions in the outer expandable members. A device can include the inner expander having an outwardly flared proximal portion that can interlock with the proximal end of the outer expandable members. A device can include a locking bridge expandable with an expandable body, such as an inflatable balloon, and movable to a locked expanded configuration. A bone fusion system, a bone fusion device kit, and/or a method for fusing bone can include such a bone fusion device.