Where and when in the world did socialism, sociology, Marxism, fascism, communism, capitalism and "freedom of speech" first collide?

Significance and the 1900 Congresses (Conferences) in Paris

Paris World Fair (Exposition Universelle de 1900), April 15 - November 12; https://www.nga.gov/features/slideshows/Exposition-Universelle-de-1900.html

DuBois exhibit
Neal’s guide https://library.si.edu/digital-library/book/pictorialdescri00

Olympics, May 14 - October 28; https://olympics.com/en/olympic-games/paris-1900
Congress of Mathematicians, August 6 - 12; Hilbert lectures delivered in French at joint session of teaching and history https://mathshistory.st-andrews.ac.uk/ICM/ICM_Paris_1900/
Socialist Congress, September 23 - 27; agenda on reformism and colonialism (socialists questioning role in bourgeoisie governments) and the relationship of socialism to labor https://library.fes.de/si-online/jugend-intro-en.html

“The International Socialist Congress in Paris in 1900 took up the question of youth or how to organize young people and was seen as part of and dealt with in connection with the struggle against militarism. The congress adopted a resolution appealing to all parties to organize young people in opposition to militarism.”