NATO Burden-Sharing: Deployment-Based Commitment Indicator (2004–2018)

Problem: Traditional measures of NATO burden-sharing, primarily military spending as a percentage of GDP, are insufficient and misleading for understanding actual commitment.
Proposed Solution: Authors introduce a public-goods-based indicator: out-of-area NATO troop deployments adjusted for population.
Key Finding: Deployment-based commitment is highly unequal. Wealthier states, those with higher military spending, and newer member states tend to deploy more relative to their size.
Implication: The 2% of GDP target (2006) does not reliably reflect commitment; a plural set of indicators is needed for a fuller picture of alliance contributions.

Commitment: Defined as willingness to provide public goods through military deployment to alliance missions abroad.
Public vs. Private Goods: Deployments to out-of-area missions are seen as public goods (benefiting the alliance), whereas military spending can often serve private, domestic interests.
Primary Measure (Deployment Indicator): Number of troops deployed to out-of-area NATO missions per 100,000 population. Formula: $ext{DeploymentRate}<em>{i,t} =\frac{ ext{TroopsDeployed}</em>{i,t}}{ ext{Population}_i} imes 10^5$
Scope: Data from 2004–2018, covering 27 NATO members (Iceland excluded). Missions included: Afghanistan (ISAF/Resolute Support), Kosovo Force (KFOR), Bosnia (SFOR/legacy), NATO Training Mission-Iraq (NTM-Iraq).
Control Variables: Wealth (logged GDP per capita), Military Capacity (military spending % of GDP, logged active-duty personnel), Alliance Seniority (Years in NATO), and various Threat Measures (e.g., coastline length, terror attacks, distance to Russia).

Rationale: Out-of-area deployments signal a direct, costly, and risky commitment to NATO's collective security beyond homeland defense, making them a clearer public-good contribution than budgetary figures alone.
Limitations:
- Not all deployments are equally intense or risky.
- Some contributions to alliance public goods occur outside formal NATO missions.
- The indicator should complement other measures; it's not a complete picture.
- The study is primarily correlational, and does not fully capture domestic political constraints or causal mechanisms.

Wealth (Hypothesis 1): Strong support. Wealthier NATO members deploy at significantly higher rates. A one-unit increase in log GDP per capita is linked to higher deployment rates.
Military Capacity (Hypothesis 2): Mixed support. Military spending as a share of GDP is positively, though modestly, related to deployment rates. Military size is not consistently linked.
Alliance Seniority (Hypothesis 3): Opposite of expectation (Reversed). Newer members consistently deploy at higher rates than long-standing members, suggesting they signal commitment to secure alliance backing.
Threat Measures (Hypothesis 4): Little to no support. External threat levels (e.g., coastline, land border, terror attacks, distance to Russia) do not consistently predict out-of-area deployment rates.
Key Examples: Slovenia, Denmark, the USA, and the UK demonstrate high deployment rates relative to spending. France and Turkey show high military expenditures but deploy at below-average rates.
Spending vs. Deployment: The correlation between average deployment rate and average military expenditure is weak ( $r hickapprox 0.15$ ), indicating spending does not reliably predict deployments.

The deployment indicator offers a vital, complementary measure of alliance commitment that better reflects the public goods nature of NATO missions than spending-based indicators.
Substantial and systematic disparities in deployment exist, challenging assumptions about burden-sharing (e.g., long-time members do not necessarily bear more burden).
The study advocates for a plural set of indicators to capture the full spectrum of NATO commitment, informing policy debates beyond the 2% of GDP rule.
Replication data and code are openly available at http://www.prio.org/jpr/datasets (Stata 16.1).