A group or parties that share a common destiny or fate and are mutually affected by each other's circumstances (literally, a 'community of shared fate').
小さな漁村では、住民全員が運命共同体のように助け合っている。
In a small fishing village, all the residents help one another as if they were a community sharing the same fate.
政府は両国を運命共同体だと呼び、協力を呼びかけた。
The government called the two countries a community of shared destiny and appealed for cooperation.
会社のリストラを機に、社員の間で自分たちは運命共同体だという意識が強まった。
Following the company's restructuring, employees' sense that they are in the same boat (share the same fate) strengthened.