Which political movement sought the unification of all Slavic peoples?

The political movement that sought the unification of all Slavic peoples is Pan-Slavism. Originating in the 19th century, Pan-Slavism aimed to unite the various Slavic nations and ethnic groups in Europe through cultural and linguistic commonalities. This movement was particularly prominent in the context of the political changes and nationalist sentiments that emerged during the decline of empires like the Austro-Hungarian and Ottoman Empires. Proponents of Pan-Slavism believed that Slavic peoples shared a unique identity that warranted political solidarity and cooperation.

The other options do not specifically target the unification of Slavic peoples. Nationalism is a broader ideology focused on the interests and culture of specific nation-states, which may not necessarily include Slavic unity as its goal. Socialism emphasizes class struggle and economic equality rather than ethnic or national unity. Fascism, on the other hand, is characterized by authoritarian nationalism and often seeks to promote the superiority of a particular nation or race, but it does not advocate for the unification of Slavic people specifically. Hence, Pan-Slavism is correctly identified as the movement that sought the cohesive unification of Slavic peoples.