A military alliance is an alliance that is made with the express purpose of military matters and promises the defense of all of its members.

• Medic Wars
  • Hellenic League - Athens, Lacedemonia, Macedon, others
• Peloponnesian War
  • League of Delos - Athens, Chios, Samos, Lesbos, others
  • Peloponnesian League - Lacedemonia, Corinth, Elis, others
• Wars of Scottish Independence
  • Auld Alliance - Scotland, Norway, France
• Italian Wars
  • League of Cambrai - The Papal States, France, Aragon, Holy Roman Empire
  • Catholic League (Italian) - The Papal States, Venice, England, Aragon, Holy Roman Empire
• Schmalkaldic War
  • Schmalkaldic League - German Protestant States
• Anglo-Portuguese Alliance - England (succeeded by the United Kingdom) and Portugal, since 1373
• Luso-Islamic War
  • Ethio-Portuguese Treaties - Portugal, Ethiopia
• Thirty Years' War
  • Catholic League (German) - Bavaria, other Catholic German States
  • Protestant Union - Protestant German States
• War of the Grand Alliance (Nine Years War)
  • League of Augsburg - The Netherlands, Holy Roman Empire, Spain, Austria, other German states
• War of the Spanish Succession
  • The Quadruple Alliance of 1718
• Napoleonic Wars
  • The Quadruple Alliance of 1814/15
  • First through Seventh Coalitions
• The Quadruple Alliance of 1834
• Anglo-Japanese Alliance - United Kingdom and Japan
• World War I
  • the Entente and the Allies - United Kingdom, France, Serbia, New Zealand, Australia, Russia (to 1917), Romania (from 1916), United States (from 1917)
  • the Central Powers - German Empire, Austria-Hungary, Ottoman Empire, Bulgaria
• World War II
  • the Axis - Nazi Germany, Empire of Japan, Fascist Italy, and many others.
  • the Allies - United Kingdom and the Commonwealth, Free France, United States, Soviet Union, Republic of China, many others.
• Cold War
  • Western European Union (WEU) - currently in process of merging into CFSP and ESDP (see below)
  • North Atlantic Treaty Organisation (NATO) -- United States, Canada, most of Western Europe (still an active alliance)
  • Warsaw Pact - Soviet Union, East Germany, Bulgaria, Hungary, Poland, Czechoslovakia, Romania
  • Southeast Asia Treaty Organisation (SEATO) - United States, United Kingdom, France, Australia, Burma, New Zealand, Pakistan, Thailand, Philippines
  • Central Treaty Organisation (CENTO) - United States, United Kingdom, Turkey, Iran, Iraq, Pakistan
  • ANZUS - United States, Australia, New Zealand (still an active alliance)
  • Five Powers Pact - Australia, Malaysia, New Zealand, Singapore, United Kingdom (still an active alliance)

• North Atlantic Treaty Organisation (NATO) - United States, United Kingdom, Canada, most of Western Europe and Central Europe, parts of Eastern Europe, and Turkey.
• Collective Security Treaty Organization (CSTO) - Russia, Belarus, Armenia, Kazakhstan, Kyrgyzstan, Tajikistan
• Common Foreign and Security Policy (CFSP) and European Security and Defence Policy (ESDP) of the European Union.
• Five Power Defence Arrangements (FPDA) - United Kingdom, Australia, New Zealand, Malaysia, Singapore.
• ANZUS Treaty (ANZUS) - United States, Australia, New Zealand.
• ECOMOG of Economic Community of West African States Monitoring Group.
• Council for Peace and Security in Central Africa (COPAX) of Economic Community of Central African States.
• Inter-American Treaty of Reciprocal Assistance (Rio Pact) - Most of the countries of the Americas.
• North American Aerospace Defense Command (NORAD) - United States and Canada. NORAD and other defense agreements (such as the Permanent Joint Board on Defense) form the most extensive defense alliance in the world.
• Regional Security System (RSS) - several Eastern Caribbean countries.
• Shanghai Cooperation Organisation (SCO), political, economic and military organisation - China, Russia, India, Pakistan, Kazakhstan, Kyrgyzstan, Tajikistan, Uzbekistan.
• Brazil, Russia, India, China, South Africa (BRICS) - economic and military assistance.