Alliances are among the oldest tools of statecraft. States join together because few of them are strong enough to stand alone against every possible threat. Yet the same alliances that deter one war can help start another. This article looks at three moments in modern history, the Concert of Europe, the alliance system before 1914 and the Cold War blocs, and draws out lessons that apply both to real diplomacy and to strategy games such as Geopolitics.

Deterrence in one paragraph

Deterrence means persuading a potential attacker that the cost of an attack will be higher than any gain. An alliance deters when it makes an attack on one member look like an attack on many. For that to work, three things must be true: the allies must have enough combined strength, the attacker must know about the commitment, and the attacker must believe it will be honoured. The third condition, credibility, is the hardest. Words are cheap; what convinces is evidence that allies are willing to pay a price for each other.

The Concert of Europe: managing great powers

After the Napoleonic Wars, the victorious powers met at the Congress of Vienna in 1814 and 1815 to rebuild the European order. Austria, Prussia, Russia and Britain, soon joined by France, agreed to consult each other in regular congresses and conferences on matters that threatened the peace. The Concert of Europe was not a formal alliance with a common army. It was a habit of consultation among great powers that accepted a rough balance between them.

For several decades it helped contain crises without a general war. Its weaknesses were also clear. It served the interests of the great powers, often at the expense of smaller nations and popular movements, and it depended on the willingness of a few governments to keep talking. The Crimean War of 1853 to 1856, in which several great powers fought each other, showed that the habit had broken down.

Lesson: regular communication between rivals can prevent misunderstandings, but it works only while the main players value the system more than any single advantage.

Before 1914: when alliances became tripwires

In the later nineteenth century, the German chancellor Otto von Bismarck built a web of agreements designed to keep France isolated and to prevent a war on two fronts. The Dual Alliance with Austria-Hungary in 1879 became the Triple Alliance with Italy in 1882, and a secret Reinsurance Treaty with Russia in 1887 kept St Petersburg close. After Bismarck left office in 1890, the treaty with Russia was not renewed. France and Russia concluded an alliance in the early 1890s, Britain and France reached the Entente Cordiale in 1904, and an Anglo-Russian agreement followed in 1907.

Europe was now divided into two camps. Military plans, especially those that depended on rapid mobilisation, meant that a crisis in one place could quickly involve every power. In the summer of 1914, the assassination of Archduke Franz Ferdinand in Sarajevo set off a chain of ultimatums and mobilisations that turned a regional conflict into a world war. Historians still debate the responsibility of each government, but many agree that rigid commitments and short timetables left little room for diplomacy.

Lesson: alliances can bind you to a partner's quarrels. Before committing, ask not only who protects you, but whose conflicts you may be drawn into.

NATO: a commitment made credible

The North Atlantic Treaty was signed in Washington in April 1949 by twelve countries. Its Article 5 states that an armed attack against one or more members shall be considered an attack against them all. The wording leaves each member to decide what action it deems necessary, yet the alliance became one of the most durable in history.

Credibility came from more than the text. Members built integrated command structures, held joint exercises and stationed forces on each other's territory. Troops deployed near a potential front line acted as what strategists call a tripwire: an attacker could not avoid fighting several allies at once. Article 5 has been invoked only once, after the attacks of 11 September 2001 on the United States.

The alliance has also faced constant debates about burden sharing. In 2014, at the Wales summit, members reaffirmed a guideline of spending 2 percent of GDP on defence, a target that many did not meet for years.

Lesson: a commitment is believed when it is backed by visible preparation and shared costs, not only by signatures.

The Warsaw Pact: an alliance with one centre

The Warsaw Pact was founded in 1955 by the Soviet Union and seven Central and Eastern European states, shortly after West Germany joined NATO. On paper it mirrored the Western alliance. In practice it was dominated by Moscow, and its forces were used against its own members: troops from several Pact countries entered Czechoslovakia in 1968 to end the Prague Spring. Albania left the same year. When the political systems of Central and Eastern Europe changed after 1989, the alliance lost its purpose and was formally dissolved in 1991.

Lesson: an alliance held together by one dominant member's pressure is less stable than one that its members choose freely. When the pressure weakens, the alliance can disappear.

Five lessons for strategists

  • Deterrence depends on credibility: preparation and shared costs matter more than promises.
  • Every commitment has a price, including the risk of being drawn into a partner's conflict.
  • Alliances that members value stay strong; those maintained by pressure are brittle.
  • Aggression often creates the very coalition the aggressor fears.
  • Talking to rivals, as the Concert of Europe did, reduces the risk of accidental war.

How alliances work in Geopolitics

In Geopolitics, every private world starts with the real membership of 18 international blocs, three of which carry a mutual defence clause: NATO, the CSTO and the European Union through Article 42.7 of its treaty. Alliances open at the third state level.

You can apply for membership in NATO, the CSTO or the EU if your country meets the conditions: it lies in the treaty area, is at peace, votes broadly like the members, has good relations with them and a decent reputation. Military alliances also require defence spending of at least 2 percent of GDP, while the EU requires stability. Applying costs political influence. The members vote after three weeks of game time, and any member with poor relations with you can veto the application, a mechanic that makes every bilateral relationship count. Membership brings prestige and better relations, but also costs: when an ally is attacked, you contribute to its defence.

AI governments react to threats as history suggests they would. If your reputation falls too low or you mass troops on a neighbour's border, nearby states seek protection by joining an alliance or signing mutual defence pacts with each other. Attack a partner and you are expelled from the alliance you share. The fifth lesson above is built into the game: an aggressive player tends to create a coalition against itself.

To learn the day-to-day side of diplomacy, read diplomacy and alliances: build your influence. For non-military pressure, see how economic sanctions work. Then take charge of a country and decide whose side you are on.