allow to search within a large set of repositories by their description. They do not search the content at a data-level.
RE3Data is a database of repositories and platforms that contain data. As you are searching for data repositories and not for datasets, you are doing an indirect search and use broad search terms. For example, by searching 'economic AND social AND history', 30 repositories containing data on this topic appeared as a result on April 22nd 2022.
Based on the information provided about the repositories you can do a direct search with more specific keywords to see if the selected repository contains useful data.
In RE3data has the option to browse or to filter results by subject ('History').
A way to narrow down results is to first search with broad keywords (i.e. economic AND social yielded 138 results on April 22nd 2022) and then filter these results by subject ('History'). This combination of keywords and filter by subject on 'History' yielded 14 results.
In RE3Data it is also possible to filter on country. This filter applies to the country of origin of the repository, which does not mean it only contains data on the that specific country. The IISH Dataverse for example, is based in the Netherlands, but contains data about a great number of countries.