这句话的that是引导同位语从句吗?When reformers in the northern states put pressure on Congress not to permit slavery in western territories ( that) later became states,some of the southern states wanted to secede,or withdraw,from the United States.这里的that引导的 later became states是同位语从句吗?还是引导定语从句呢？感觉应该是定语从句，that 在定语从句中作主语。

这句话的that是引导同位语从句吗?
When reformers in the northern states put pressure on Congress not to permit slavery in western territories ( that) later became states,some of the southern states wanted to secede,or withdraw,from the United States.
这里的that引导的 later became states是同位语从句吗?
还是引导定语从句呢？感觉应该是定语从句，that 在定语从句中作主语。