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Comrades and Cause: Peer Influence on West Point Cadets' Civil War Allegiances

Yuchen Guo, Matthew O. Jackson, Ruixue Jia

TL;DR

This study investigates how peer networks shaped the allegiance choices of West Point cadets during the Civil War, leveraging quasi-random variation in cohort-level exposure to Free-State peers. Using detailed biographical data (1820–1860) and state-level slavery measures, the authors document a robust, asymmetric peer effect: cadets from Slave States were more likely to join the Union when more of their peers came from Free States, while Free-State cadets showed little sensitivity to peer composition. The effect operates most strongly within cohorts and among those with continuous military careers, and is attenuated in highly slave-dependent contexts or for those personally owning slaves; shared experiences such as prior war service amplify the influence. The findings contribute to the broader literature on peer effects by showing how personal networks can drive pivotal loyalty decisions in highly polarized settings, with implications for understanding leadership formation and political alignment in divided societies. The analysis also links wartime allegiances to post-war outcomes, showing a trade-off between early Union allegiance and later military rank and survival for Slave-State cadets, highlighting the long-run consequences of peer-driven decisions in conflict contexts.

Abstract

Do social networks and peer influence shape major life decisions in highly polarized settings? We explore this question by examining how peers influenced the allegiances of West Point cadets during the American Civil War. Leveraging quasi-random variations in the proportion of cadets from Free States, we analyze how these differences affected cadets' decisions about which army to join. We have three main findings. First, there was a strong and significant peer effect: a higher proportion of classmates from Free States significantly increased the likelihood that cadets from Slave States joined the Union Army. Second, the peer effect varies with geography, most notably with the slave population share in cadets' home states or counties, and with cadets' own slave ownership in 1860. Third, shared experiences -- such as having served together in the Mexican-American War, continuous military service, and belonging to the same cohort -- amplified peer effects, suggesting that sustained interaction is important.

Comrades and Cause: Peer Influence on West Point Cadets' Civil War Allegiances

TL;DR

This study investigates how peer networks shaped the allegiance choices of West Point cadets during the Civil War, leveraging quasi-random variation in cohort-level exposure to Free-State peers. Using detailed biographical data (1820–1860) and state-level slavery measures, the authors document a robust, asymmetric peer effect: cadets from Slave States were more likely to join the Union when more of their peers came from Free States, while Free-State cadets showed little sensitivity to peer composition. The effect operates most strongly within cohorts and among those with continuous military careers, and is attenuated in highly slave-dependent contexts or for those personally owning slaves; shared experiences such as prior war service amplify the influence. The findings contribute to the broader literature on peer effects by showing how personal networks can drive pivotal loyalty decisions in highly polarized settings, with implications for understanding leadership formation and political alignment in divided societies. The analysis also links wartime allegiances to post-war outcomes, showing a trade-off between early Union allegiance and later military rank and survival for Slave-State cadets, highlighting the long-run consequences of peer-driven decisions in conflict contexts.

Abstract

Do social networks and peer influence shape major life decisions in highly polarized settings? We explore this question by examining how peers influenced the allegiances of West Point cadets during the American Civil War. Leveraging quasi-random variations in the proportion of cadets from Free States, we analyze how these differences affected cadets' decisions about which army to join. We have three main findings. First, there was a strong and significant peer effect: a higher proportion of classmates from Free States significantly increased the likelihood that cadets from Slave States joined the Union Army. Second, the peer effect varies with geography, most notably with the slave population share in cadets' home states or counties, and with cadets' own slave ownership in 1860. Third, shared experiences -- such as having served together in the Mexican-American War, continuous military service, and belonging to the same cohort -- amplified peer effects, suggesting that sustained interaction is important.

Paper Structure

This paper contains 55 sections, 6 equations, 5 figures, 21 tables.

Table of Contents

  1. Introduction
  2. The Data
  3. The Cadets
  4. Geography and the Classification of States by High/Low Slave
  5. Results
  6. Descriptive Evidence
  7. Importance of Home State
  8. Relevance of Peers
  9. What Drives Variation in Peer Composition?
  10. Statistical Analysis
  11. The Impact of Peers on Cadets' Allegiance
  12. Baseline Estimates
  13. Interpreting the Asymmetric Peer Effects
  14. Variations in Peer Effects with Political-Economic Backgrounds
  15. Shared Experience and Peer Influence
  16. ...and 40 more sections

Figures (5)

  • Figure 1: Home-state slave share and the probability of joining the Union
  • Figure 2: Relevance of Peers: Motivating Evidence
  • Figure S1: Text examples
  • Figure S2: Slave share and cadet's choices
  • Figure S3: Peer influence by cohort