Those societies came out of the war with levels of enrollment that had been roughly constant at an 3%-5% of the relevant age groups during the decades before the war.
根据断句长短适中、语法长度完整的原则，我们可以把这句断成3个部分如下：
① Those societies came out of the war
②with levels of enrollment that had been roughly constant at an 3%-5% of the relevant age groups
③ during the decades before the war.
分析各部分的结构：
① 主语(Those societies )+谓语(came out of )+状语(the war)
② 状语：with levels of enrollment+定语从句( that had been roughly constant an 3%-5% of the relevant age groups )
③ age groups 的定语：during the decades before the war..
参考译文：这些社会从战争中走出来，当时的入学情况和战前几十年的情况处于相同水平，一直维持在适龄人群的3%-5%左右。