A more thorough explanation:

Retaliatory measures, also known as reprisals, refer to the actions taken by a country in response to similar actions taken by another country. These measures can be diplomatic or involve the use of force, and are considered lawful under international law principles.

Retaliatory measures are taken when a country wants to respond to unfriendly behavior, whether it is legal or not. The measures taken are intrinsically lawful and in conformity with international law. For example, a country may choose to rupture diplomatic relations or impose economic sanctions in response to similar actions taken by another country.

One example of retaliatory measures is the tit-for-tat tariffs between China and the United States during the Trump presidency. When the United States imposed tariffs on Chinese goods, China responded by imposing tariffs on American goods. This back-and-forth exchange of tariffs is an example of retaliatory measures.

Another example of retaliatory measures is the suspension of diplomatic relations between countries. For instance, when North Korea conducted nuclear tests, several countries, including the United States, suspended diplomatic relations with North Korea in response.