Pre WW2 Europe was full of (state backed) cartels and monopolies. These were dismantled for the most part.

A lot of these were international. Just read up on "Cartel capitalism".

https://www.cambridge.org/core/journals/enterprise-and-socie...

The European Steel and Coal Community (precursor of the EU) was also involved in the effort to stop these. In general this has been something the EU has been involved in since its inception and the best action against monopolies is to not let them form in the first place (why there is so few of them in general in most developed countries. Though that is now slowly changing it seems)

Look into the mechanisms being worked on to create competition in rail operators (which has been opening the markets to competitor rail operators)