Key events in diplomatic relations?

Which countries and time period are you asking about? The key events in diplomatic relations between any two countries depend on their shared history, so a specific pair—such as India and China, or the United States and Cuba—would make the question easier to answer.

In general, a diplomatic timeline often includes the establishment of diplomatic ties, major agreements or the signing of a peace treaty, high-level state visits, periods of tension or crisis, and efforts at normalization of relations. In severe disputes, countries may recall ambassadors or resort to breaking diplomatic relations.

If you share the countries or region you have in mind, I can list the most significant events in order and briefly explain why each mattered.