How could World War 3 start? Five scenarios explained

World War 3 could start if a regional war brings major powers into direct fighting and expands into other regions. A Russia–NATO clash, a conflict over Taiwan, a wider Middle Eastern war or renewed war in Korea could create that danger. Another possibility is that several crises become connected through the same countries and alliances.

The starting point would matter less than the decisions that followed: whether another country joined the fighting, whether attacks spread, and whether the governments involved could stop the exchange. The five scenarios below explain those possible pathways using events from the conflict timelines.

1. The Russia–Ukraine war expands into a Russia–NATO war

Russia’s full-scale invasion of Ukraine began on 24 February 2022. NATO countries have supported Ukraine, while the alliance has reinforced its own territory. Ukraine is not a NATO member, so attacks on Ukraine and attacks covered by NATO’s collective-defence treaty involve different commitments. Russia–Ukraine timeline; NATO membership.

The escalation scenario is a sustained exchange between Russia and NATO forces. It could develop after an attack on allied territory, a clash involving aircraft or ships, or a decision to strike forces supporting one side of the war.

An actual example of the pressure appeared in September 2025, when Russian drones violated Polish airspace. Poland requested Article 4 consultations with its allies. Those consultations brought the incident into NATO’s political decision-making process. NATO’s Article 4 record.

For a larger war to follow, governments would still have to make further decisions about force. Repeated attacks and retaliation could create a cycle in which each side treated the other’s response as justification for its next action.

The route to containment would involve stopping that cycle: establishing responsibility, communicating limits and preventing a further encounter from creating another demand for retaliation. Follow the sequence in the Russia–NATO timeline.

2. A Taiwan conflict brings China and the United States into combat

A Taiwan crisis could involve an invasion, attacks on military infrastructure, or an attempt to restrict the island’s access to the outside world. A blockade would raise a particularly difficult question: what happens if another country tries to keep commercial access open and its forces meet resistance?

The Taiwan Strait has already experienced dangerous confrontations. During the 1995–1996 crisis, China conducted missile tests and exercises near Taiwan, and the United States deployed carrier groups. The crisis ended without an invasion. China–Taiwan timeline.

In a future conflict, a US decision to intervene could turn fighting over Taiwan into direct China–US combat. Japan could face further decisions if its territory or facilities came under attack. Its security treaty with the United States addresses attacks against either party in territories under Japanese administration. Japan–US treaty.

The dangerous transition would be from a dispute about Taiwan to sustained attacks involving additional states. Restored access, a halt to military action and an agreement about the immediate confrontation could interrupt that transition.

The outcome would depend on what the participants did. An exercise that rehearses a blockade is still different from an enforced restriction on real shipping.

3. Middle Eastern wars expand through direct attacks and foreign bases

This pathway has an established regional precedent. In June 2025, the United States struck Iranian nuclear facilities. Iran then attacked Al Udeid Air Base in Qatar. A confrontation involving Israel and Iran had drawn in direct US military action and an attack on a base in another country. US acknowledgement of its strikes; Iran–Gulf timeline.

The global escalation scenario would go further: repeated attacks involving more states, prolonged fighting over commercial routes, or a confrontation drawing in another major power.

Foreign bases are important because the country hosting a base and the country operating forces there have different roles. An attack can affect both, while leaving each government with its own decisions about defence and retaliation.

Shipping adds a second connection. Disruption around the Strait of Hormuz or the Red Sea can affect energy supplies and trade far beyond the battlefield. Governments may respond with diplomacy, naval protection or military force. The economic effects can spread much further than the fighting itself.

Containment depends on agreements that address the immediate attacks and on the parties’ willingness to observe them. A pause in one campaign can help even while other disputes remain unresolved.

4. Renewed war in Korea draws in outside powers

The Korean Peninsula remains divided under an armistice framework. The 1953 agreement stopped large-scale hostilities; it did not produce a peace treaty. The conflict has also seen later armed incidents, including North Korea’s shelling of Yeonpyeong Island in November 2010 and South Korea’s return fire. Korea timeline.

A renewed large-scale attack would immediately raise questions under the US–South Korea defence relationship. A longer war could force additional decisions by neighboring powers about their own security and involvement.

The most dangerous outcome would combine expanding conventional fighting with nuclear threats and failed communication. The existence of nuclear weapons raises the stakes, but it does not predetermine every military decision.

Stopping an initial exchange, keeping military channels open and limiting the geographic scope of action would be central to preventing a broader conflict.

5. Several crises become one connected confrontation

Connections can form before a new front opens. In October 2024, NATO confirmed that North Korean troops had been sent to Russia and units deployed to Kursk. That created a concrete military link between European and Korean security. NATO statement.

A future crisis could add more links. The same government might face a war in one region and an allied request for protection in another. A decision to move forces, enter combat or retaliate against a shared opponent could join previously separate confrontations.

This scenario does not require a single plan agreed in advance. It could emerge from a sequence of decisions, each taken in response to the last.

Could any of these scenarios be avoided?

Yes. None of the pathways makes World War 3 inevitable. They identify the steps through which a wider war could develop—and therefore the points at which it could be contained.

The decisive changes would be additional major powers entering combat, sustained fighting spreading across regions and agreements failing to halt it. For the current assessment and the events behind it, see the global conflict tracker.