Use 'federate' to discuss countries or states forming a union, usually for governance. After the agreement, the regions will federate to enhance their international standing.
Pro Tip 2/3
Joining Forces
'Federate' implies coming together for mutual benefit and often indicates increased strength. Several small organizations may federate to have a more significant impact.
Pro Tip 3/3
Voluntary Union
'Federate' usually means a voluntary alliance, not one that is forced or coerced. The companies agreed to federate rather than merge, maintaining their independence.