Which groups were missing in the Constitution? How does this reveal a contradiction in this document?

There really are very few specific identity groups, as we would think about them today, mentioned in the original Constitution, and none are mentioned extensively. Even enslaved African Americans were only mentioned euphemistically as "other persons" (in the notorious 3/5 compromise), a "person held to service or labor" in the Fugitive Slave Clause, and, even more obliquely, as "persons" subject to "importation" in a clause referring to the slave trade. Native Americans were only mentioned in a clause empowering Congress to regulate trade with them. Women are not mentioned at all.
What this tells us is that the Constitution was a product of its time, and that it was not intended to promote freedom for African Americans, equality for women, or recognition of land rights for Native Americans. It was a document, rather, created by and for white male landowners and even at that was seen by many lower-class white men as a threat to their well-being; they feared that the consolidation of the federal union would lead to policies that privileged the wealthy (especially creditors) over their interests.
We view this as a contradiction today, but it was simply not viewed in that sense by the vast majority of eighteenth- and early nineteenth-century white land-owning men. These contradictions eventually emerged with force in the nineteenth century, as abolitionists in particular criticized the Constitution as a "covenant with death" due to the fact that it countenanced slavery.
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