Is the interstate commerce act a valid example of pure socialism?
No it is not. The reason it's not is this is that Socialism has to do with ownership of the means of production and distribution, which means how the surplus value generated by the means of production is used.
the Interstate Commerce act has nothing to do with socialism.
It is an example of government interventionism in a market-based economy. It did not attempt to change the method of ownership and allocation of surplus value in the railroad industry, nor did it attempt to introduce worker self-management.
The Celts were not an unified state but rather a group of numerous tribes that often didn't even speak the same language. They were found all around Europe and were mostly Warriors who build their societies around kinship. They were good farmers and mostly were common people. They didn't have a strong unified state because they lived day in day out, women would give birth to children and men would work on the land and occasionally fight against invaders. There was no spirit of a great Celtic nation.