Since World War II, the United States has taken on policing roles in several situations. The first example was with the conflict in Korea. When North Korea invaded South Korea in 1950 without provocation, the United States went to the United Nations to take actions to stop this invasion. With the United States taking a leading role, the United Nations sent forces to help South Korea repel the invasion by North Korea. When the conflict ended, Korea remained divided. The United States to this day helps South Korea.
Another example of a police action was our involvement in the first Iraq war in 1990-1991. Iraq had invaded Kuwait in a border dispute. The United States along with the United Nations led the effort to remove Iraq from Kuwait. This was successfully accomplished in 1991.
A third example of a police action was when the United States along with NATO entered Serbia to keep the peace there. There was a civil war occurring between the Albanians and the Serbs in the province of Kosovo. Encouraged by the United States, NATO attacked the Serbs to stop the killing of the Albanians in the province of Kosovo.