Surveys show that the fraction of disk galaxies hosting large-scale stellar bars declines toward higher redshift and that dynamically mature, long bars already exist at z ? 1–3, earlier than many ΛCDM-based models expected for cold, stable disks (Sheth et al. 2008; Melvin et al. 2014). Simulations in ΛCDM can form bars, but often either predict too many strong bars at low redshift or require finely tuned disk stability, gas fractions, and merger histories to match the observed redshift evolution and early appearance of substantial bars, highlighting a tension between simple hierarchical expectations and the complex, environment-dependent bar fraction evolution seen in data (Kraljic et al. 2012; Melvin et al. 2014).