Most ethical frameworks work well within a civil society but have a tendency to break down as soon as relationships outside that society are involved. The greatest example is war.
If your enemy is attempting to destroy you, don't you have every right to defend yourself? This is where the idea of competition versus cooperation becomes valuable.
The government and the laws of a country are examples of cooperation. The government combines millions of people together in order to create a playing field where these people can cooperate.
For example all the people in a country generally agree that within the country killing is bad and that stealing is bad. The building of roads and other infrastructure are other obvious examples of cooperating through government.
A slightly less obvious example of rules as a form of cooperation is the stock market. The stock market is often seen as the king of competition. Yet there is cooperation in setting the ground rules for trading, cooperation in disseminating information and following the rules for settlement.
Within this rules based cooperative framework there is competition. There is competition in labour markets, competition between different products, competition while driving and competition when buying a house. Any time a person looks after their own interests above others that is competition, whether or not the competition is economic.
The cooperation and competition dynamic may also be used to examine our relationship with animals and the ecosystem more broadly. Our relationship with cattle and poultry is one of cooperation: we eat the animals (or consume other products from them) and in return we have boosted their population.
Our crops are pollinated by bees which receive nectar in return. On the other hand animals which are a direct danger to humans, such as tigers in India or wolves in Europe, are competing with humans and have been virtually eliminated from those areas. In other senses animals may compete with humans. Humans and animals often compete for land. "Pests" such as mice, cockroaches and flies compete with us for food.
War is the ultimate competition. War is competing for our lives. Very little "ethics" or "cooperation" survives war. War needs its own article but I will give some examples to show why competition versus cooperation is a suitable mental construct to consider the ethics of war.
The Geneva conventions provide a basic level of cooperation during wartime. However the Geneva conventions have on occasion been found to require significant changes to remain relevant - particularly in 1949 after world war 2 and in 1977 with the signing of protocols 1 and 2.
The Geneva conventions protect civilians from deliberate attack (collateral damage is still permissible under the conventions) and treatment of prisoners. Other rules include how to indicate that one party wishes to negotiate a surrender or a truce.
One motivation for soldiers to follow the Geneva conventions is that of self-preservation. For example if one army mistreats, tortures or kills prisoners of war, the other side is likely to either not surrender as easily or mistreat prisoners of war in return.
So cooperation through the Geneva conventions for the basic human necessities are (mostly) adhered to due to self interest. The payback is still there but it only covers the basic necessities, though it does not even cover the most important necessity - life itself.
