Sometimes non-aggression pacts and neutrality pacts have been considered different. In that case non-aggression pact is considered to include the promise not to attack the other signatories, while a neutrality pact includes a promise to avoid any support against the other signatories. In 19th century neutrality pacts have often been used to give permission to attack another state.
It was a popular form of international agreement in the 1920s and 1930s, but has largely fallen out of use after the Second World War. Since the implementation of a non-aggression pact depends on the good faith of the parties, the international community following the Second World War adopted the norm of multilateral collective security agreements, such as the treaties establishing NATO, ANZUS, SEATO and Warsaw Pact.
An example of non-aggression pact is the 1939 Molotov–Ribbentrop Pact between the Soviet Union and Nazi Germany, which lasted until the 1941 German invasion of the Soviet Union in Operation Barbarossa.
- Volker Krause, J. David Singer "Minor Powers, Alliances, And Armed Conflict: Some Preliminary Patterns", in "Small States and Alliances", 2001, pp 15-23, ISBN 978-3-7908-2492-6 (Print) ISBN 978-3-662-13000-1 (Online) 
- Brett Leeds , Jeffrey Ritter, Sara Mitchell, Andrew Long, "Alliance Treaty Obligations and Provisions, 1815-1944", "International Interactions: Empirical and Theoretical Research in International Relations", 2002, vol. 28, issue 3, p. 237-260, DOI: 10.1080/03050620213653