The United Nations Extrasolar Conflict Resolution Organisation (UNECRO) was established in 2047 during the initial colonisation boom. Its mandate is to prevent fighting outside the solar system: initially it stepped between competing corporations, but more recently it has also become involved in the affairs of newly-independent colonies.
Typically units of national militaries are rotated to UNECRO duty at the batallion level for one to three years. Since actual deployments are usually rather smaller, more recent developments have seen small units and even individuals being mixed into a "multi-disciplinary force". It remains to be seen how well this will work in practice; detachment to these units, having a rather higher risk than earthbound soldiering, is not welcomed by the troops, and "Walking Corpses" is one of the more polite terms in use for them.