Short birth intervals are associated with increased mortality in challenging settings, and the objective here was to explore the significance of birth spacing relative to the neonatal, postneonatal, and early childhood mortality for rural Mennonites from one congregation in two settings: Russia, 1825-1874, and Kansas, 1875-1924, in light of two causal mechanisms: maternal depletion and sibling competition. Vital events of families reconstructed from church records comprised a total of 930 and 1,484 births in Russia and Kansas, respectively, by 381 mothers. Bivariate analyses indicate that mortality is higher in Russia relative to Kansas for births with the shortest previous intervals for all three age categories, and for neonates born before the shortest subsequent intervals. Cox regression analyses indicated that only a few factors played a statistically significant role. Mortality risk was increased in Russia by having mothers >35 years and shorter subsequent intervals for the neonates, shorter subsequent intervals for the postneonates, and having mothers >35 years, and shorter previous and subsequent intervals for early childhood. In Kansas, mortality risk was increased by shorter subsequent intervals and being a member of a multiple birth for neonates, shorter previous and subsequent intervals and being a member of a multiple birth for postneonates, and being a member of a multiple birth, when the preceding child dies, and a shorter subsequent interval for early childhood. The increased risk in Russia associated with being born to an older mother and the increased risk in the total sample for the older age categories with the shortest previous intervals provide moderate support for the maternal depletion hypothesis. That longer subsequent intervals increase survivorship in all settings for all age categories provides limited support for the sibling competition hypothesis.