"Usually sources are complied from historical links."
By far the largest 'source' available on the Ancestry.com site is MemberTrees. There are other genealojunk database indexes based on some outfit's compilation from such things as submitted family group sheets and/or sundry published genealogical accounts, which similarly have no more specific source given than the outfit from which the index was acquired.
Ancestry.com explained the general source of the database index acquired under title of "Millenium File." Ancestry.com did not acquire the reports and working files compiled by the consultant that might (or might not) give source details. It is very unlikely that much of the source material would be posted on the internet, either as an Ancestry.com database or by some kind volunteer on such website groups as USGenWeb.
FamilySearch's International Genealogical Index, Ancestral File and Pedigree Resource File are mostly compiled from submitted family group sheets which might or might not be based on any evidence. They have been a ~source~ for many trees, but are of the same character as other trees on the internet and such compilations as the "Millenium File."
You are making a step forward in the desire for source-citations. But you won't find them specifically related to particular events and relationships within junk database indexes.
If you want genealogy based on evidence, there are no shortcuts for doing the records-research yourself. Most records are not accessible on the internet.