A recognized enemy may be aided to compromise or appease them and/or to indirectly or directly aid oneself or own side, for instance by supporting the "lesser of the two evils" to undermine an undesirable outcome. Such activities tend to be secretive and can be dirty and complex.
With the change in regimes in eastern Europe and the collapse of the former USSR, the release of secret police and similar files led to the exposure of many individuals as collaborators. Public trials began in Kuwait in 1991 of 628 alleged collaborators suspected of aiding the Iraqi forces during the Iraqi invasion of Kuwait. The accused were mainly Palestinians and Iraqis, and regarded by many as innocent victims of the public need for vengeance. One example of Vichy French collaboration during World War II was the arrest by Paris police of some 13,000 Paris Jews for deportation to the Nazi concentration camps. There were around 4,000 children included. About 400 survived the war. France's Roman Catholic Church has also been accused of fully supporting the Nazi government of Vichy France.
In the mid-1950s, the pacifist Fellowship of Reconciliation in the USA, learning of famine on the Chinese mainland, launched a 'Feed Thine Enemy' campaign. Members and friends mailed thousands of little bags of rice to the White House with a tag quoting the Bible, "If thine enemy hunger, Feed him." As far as anyone knew for more than ten years, the campaign was an abject failure. The President did not acknowledge receipt of the bags publicly; certainly, no rice was ever sent to China. What non-violent activists only learned a decade later was that the campaign played a significant, perhaps even determining role in preventing nuclear war. Twice while the campaign was on, President Eisenhower met with the Joint Chiefs of Staff to consider US options in the conflict with China over two islands, Quemoy and Matsu. The generals twice recommended the use of nuclear weapons. President Eisenhower each time turned to his aide and asked how many little bags of rice had come in. When told they numbered in the tens of thousands, Eisenhower told the generals that as long as so many Americans were expressing active interest in having the US feed the Chinese, he certainly was not going to consider using nuclear weapons against them.