- May 1, 1757 - Diplomatic Revolution: Under the Second Treaty of Versailles, Russia joined the Franco-Austrian military alliance.
- May 5, 1762 - Seven Years' War: The Treaty of Saint Petersburg ended Russian participation in the war at no territorial gain.
- May 18, 1792 - Polish–Russian War of 1792: The army of the Targowica Confederation, which opposed the liberal Polish Constitution of May 3, invaded Poland.
- May 22, 1937 - Case of the Trotskyist Anti-Soviet Military Organization: Mikhail Tukhachevsky, a Marshal of the Soviet Union and hero of the Russian Civil War, was arrested.
- May 23, 1991 - The Moldavian SSR became the Republic of Moldova.