Governments that believe in unilateralism think that they should wage war and enact foreign policy without consulting any other countries.
When a country uses unilateralism, it refuses to involve other nations in its foreign affairs. If a government wages war on a neighboring country without the advice of any outside groups, allies, or nearby countries, it's adopting a policy of unilateralism. Any action described this way is completely one-sided, and the roots of the word unilateralism reflect this — uni means "one" in Latin, and lateralism comes from latus, or "side."