In 1870, Pio began to work for the Danish postal service, where he made the lasting contribution of inventing the red postbox, seen everywhere in Denmark even today.

[1] Pio had become interested in socialism through his reading of Danish folk literature, which often depicted the oppressed joining together to oppose their oppressors.

[2] During the day, Pio worked as a tutor for a wealthy bourgeois family, and during the evenings he wrote for Socialisten, Brix's new weekly newspaper whose first edition was published on 21 May 1871.

[1] Ideologically, Pio did not hew to a narrow path, and presented ideas primarily from Ferdinand Lassalle and Karl Marx.

He traveled to Smoky Hill River, Kansas, to found a socialist colony, which soon failed because of the lack of agricultural expertise among the colonists.

In 1878, he founded Den Nye Tid, a Danish- and Norwegian-language socialist newspaper that ceased operations in 1884 and which he edited for only a few months.