What Makes a Good Military Coalition Partner?

The United States Defence Secretary, Pete Hegseth, recently commented that the International Security Assistance Force (ISAF) in Afghanistan, which existed between 2001-2014, colloquially stood for ‘I saw Americans fighting’ at a recent Capitol hearing.¹ Hegseth was giving evidence in front of the Senate Appropriations Committee when he made the comment, which complements the current Trump Administration’s of America-First foreign policy,² in that European countries should not rely on American military support and that Europe should be pulling its weight more in support of collective defence. Hegseth further added that, ‘what ultimately was a lot of flags, was not a lot of ground capability, you’re not a real coalition unless you have real defense capabilities and real armies can bring those to bear and that’s a reality Europe is waking up to quickly’.³ Senator Chris Coon, a Democrat who sat on the Committee, was quick to clarify that other military partners served and died within Afghanistan.⁴ In an unpredictable world this exchange provoked a key thought, what makes a good military coalition partner, seen from a Western perspective? 

Brief History of Military Coalitions 

Forming military coalitions based on shared strategic goals is not a new concept. Pragmatically, it makes sense to form military coalitions to share capabilities/equipment, to act as a deterrence, and to form international legitimacy against any action against a common adversary. Even the mighty Spartan Army fought alongside a military alliance with other Greek soldiers when threatened by the Persian Empire in the 5th Century BCE. According to Herodotus, there were only 300 Spartan Royal bodyguards in comparison to thousands of other Greeks who fought against the Persians.⁵ However, these Spartans were portrayed as warriors who were disciplined and highly trained in comparison to other Greek soldiers.⁶ Facing a force of a hundred thousand Persian soldiers, the odds were against the Greeks. Were the Spartans a better coalition partner than the other Greeks as they had alleged quality over quantity, or was mass required? The eventual defeat of the Greeks at the Battle of Thermopylae and sacking of Athens, perhaps for this specific battle, meant that simply more Greeks were needed to match the Persians.  

Moving forward to the 21st Century, the North Atlantic Treaty Organisation (NATO) was created in 1949. ISAF was formed after the events of 9/11, when Article 5 was triggered, but it was in 2003 when NATO took the lead of the UN mission in Afghanistan. At the height of the mission, 51 NATO and partner nations provided troops.⁷ With six different ISAF objectives and the whole of Afghanistan divided into five (later six in 2010) Regional Commands, ISAF members held various roles and responsibilities. For example, Regional Command North was commanded by Germany with troops from Sweden, Hungary, and Norway supporting the various missions.⁸ Troop numbers and equipment supplied varied across ISAF, with the United States contributing the most significant number of troops by some margin. This tragically resulted in greater deaths, with the United States losing nearly 2500 military personnel in comparison to a country like Georgia, in which 29 military personnel were killed.⁹ When compared against the population size of Georgia (a non-NATO country), the deaths experienced in Afghanistan resulted in a death per million rating of 8.42, higher than the United States at 7.96. However, it is ethically challenging to compare the number of casualties experienced by each partner. As such, measuring casualty figures by each coalition partner is not an efficient way to determine if each country is ‘pulling its weight’.   

Another significant military coalition was formed in 2014. The Global Coalition against Daesh originally had 13 members, but today has 87 partners and is designed to degrade and ensure Daesh’s enduring defeat.¹⁰ In September 2014, President Obama commented in a major speech that Daesh were a threat to the United States, ‘but this is not our fight alone’.¹¹ Operation SHADER was the UK’s contribution to the United States’ Operation INHERENT RESOLVE, in which the UK Armed Forces provided valuable support and training to more than 111,000 members of the Iraqi Security Forces, including conducting 10,000 Royal Air Force sorties striking more than 1400 targets.¹² According to the United States and Iraq, battlefield gains resulted in a significant loss of Daesh territory, which will cause a drawdown of the military mission in 2025.¹³ 

Reviewing historical coalitions helps inform the contemporary analysis of what makes a good coalition partner.  

What Makes a Good Military Coalition partner? 

Throughout ancient times, the number of soldiers on the battlefield may have been a determining factor in declaring victory; however, within the modern geopolitical context, let’s consider some other attributes of a good military coalition partner: 

Partners to commit to promises made

One notable equaliser within a military coalition relates to how much money is spent on defence as a percentage. For example, back in 2014, NATO agreed that member states would spend 2% of their Gross National Product (GDP) on defence. However, nine countries are currently missing that target.¹⁴

 More recently, it has been agreed to increase that figure to 5% by 2035, with 3.5% on core defence and a further 1.5% on broader security investments. However, this commitment is not bound by any law; only political pressure exists, which has seen some countries forced to increase their defence spending. Some countries, such as Spain, have even asked for exemptions from this rise in defence spending. Was this recent NATO agreement to spend more a political play by its members to appease President Trump or an actual recognition of the threats faced by the West? Regardless, being a good military coalition partner, in this case within NATO, promises should be kept, although noting that political changes between now and 2035 have the ability to disrupt agreements.  

Leadership and the ability to step up

Evidence suggests that persuasive leadership and its subsequent unity of command within a military coalition are key in driving strategic objectives.¹⁵ Recent political intent from the United States has resulted in pressure being placed on European countries to step up in support of Ukraine, whilst the United States continues to pivot towards the Pacific. However, by their very nature, Western military coalitions are limited by each partner’s political goals and risk appetites, which in turn will be unique to each country. With the Global War on Terror between 2001 and 2021, the United States played a key leadership role within ISAF and the Global Coalition against Daesh. However, this doesn’t necessarily need to be the case. With a changing United States’ foreign policy pivot to the Pacific, there have been opportunities for European countries to step up and take the lead. We have seen that with the UK and France forming the ‘Coalition of the Willing’, which was announced by the UK’s Prime Minister on 2 March 2025, in support of security guarantees for Ukraine. Noticeably, this did not include the United States. However, it does show that European leaders have understood their need to take a leadership role without the direct support of the United States. Western military coalitions do not need to be led by the United States, but their collective 

Interoperability is key

A good military coalition partner integrates well with other partners to ensure success. Simply speaking the same language across multiple coalition partners can be challenging. From equipment integration to command and control to varying doctrines, large coalitions can be complex, which could impact strategic successes. 

NATO defines interoperability as, ‘the ability for Allies to act together coherently, effectively and efficiently to achieve tactical, operational and strategic objectives’.¹⁶ NATO has been exercising and training collaboratively since its inception and has seen so-called military successes in Bosnia, Kosovo, and Libya. But what about recently formed coalitions and their military partners’ interactions and interoperability with non-partner organisations? Using the example of the Global Coalition, in 2014 Daesh seized territory across Syria and Iraq, but by 2019, it held none.¹⁷ Evidence suggests that the Global Coalition had been a success and that combined air power from the United States and United Kingdom, alongside engagement with Iraqi and Syrian allied ground forces, was essential in Daesh’s enduring defeat.¹⁸ In this example, a combination of interoperability with partner nations, coupled with those organisations not within the coalition, was the key to success. Being a good military coalition partner ultimately means being a good team player and having the ability to work with various nations and organisations.

Conclusion

Military coalitions can be powerful and have proved to be successful throughout history, and as such, are likely to endure as countries face a diverse range of threats. The role of collective understanding and will, coupled with strengthened partnerships, will be critical for warfighting now and in the future. Being a good military coalition partner is multi-faceted, dependent on perspectives, and more nuanced than simply troop numbers in isolation. Fundamentally, it’s about following through on individual commitments (despite some not being legally binding), stepping up to take a leadership role, and working collaboratively with other partners and non-partner organisations.. The first two attributes are driven at the political level for Western military coalitions, with the third sitting across all levels of warfare. A military coalition partner may display all three attributes, but that doesn’t guarantee strategic coalition success. As Churchill famously quoted, ‘there is only one thing worse than fighting with allies, is fighting without them’. 

 

Feature image credit: MOD

1. Telegraph, Hegseth jokes about US allies doing nothing in Afghanistan – despite hundreds losing their lives, 11 Jun 25.
2. White House, President Trump’s America First Priorities, 20 Jan 25.
3. Ibid
4. Ibid
5. Herodotus, Histories 7.205.
6. Herodotus, Histories 7.234.
7. NATO, ISAF’s mission in Afghanistan, 30 May 22
8. House of Commons Library, The International Security Assistance Force in Afghanistan
9. iCausalities, Fatalities by Country
10. United States Central Command, Global Military Leaders Meet and Discuss Defeat ISIS Campaign at Combined Force Commanders’ Conference in Bahrain, 3 Feb 25.
11. USAToday, President Obama, USA TODAY 10 Sep 14.
12. British Government, UK response to the conclusion of the Global Coalition’s military mission in Iraq, 28 Sep 24.
13. Ibid.
14. BBC News, Why Trump is targeting Spain over NATO spending, 24 Jun 25.
15. The US Army War College, Kelly A. Grieco, Fighting and Learning in the Great War: Four Lessons in Coalition Warfare, Volume 48, Number 3, 2018.
16. NATO, Interoperability: connecting forces, 11 Apr 23.
17. House of Commons Library, Countering Islamic State/Daesh in Africa, Syria and Iraq 2025, 18 Mar 25.
18. RAND, The Air War Against Islamic State, 5 Feb 2021.