Military force is justified as a last resort when all other non-forceful alternatives have been exhausted.
Since Israel took the first strike (against Egypt) in 1967 as a preemptive move, it is fair to question whether it had waited for military action as a last resort or if it could have avoided war with further diplomatic efforts. Regardless, it saw itself as fighting a defensive war and only invaded the West Bank after being attacked on that front.
Military occupation is categorically difficult to judge under the criteria of last resort. Once established, a military occupation is no longer a matter of waiting to pursue other options first. However, the spirit of last resort implies that the occupying force do everything in its power to end the occupation. Israel does not seem to be following this course of action, but is instead putting its occupation on a path of further entrenchment. This decision to continue in occupation, rather than relinquish the territory, is a failure to embody the spirit of last resort.