The party that fought for peasants' rights in Russia was the Socialist Revolutionary Party (SRP).

The Socialist Revolutionary Party was a major political party in Russia during the late 19th and early 20th centuries. It was formed in 1901 as a result of a split within the Russian Social Democratic Labor Party. The party primarily represented the interests of the peasantry, which constituted the majority of the Russian population at the time.

The SRP advocated for land reform and the redistribution of land from wealthy landowners to the peasants. They believed that the peasantry, as the largest social class in Russia, should have control over their own land and resources. The party also called for the improvement of living conditions for peasants, including access to education, healthcare, and social welfare programs.

The SRP was deeply involved in the revolutionary movements in Russia, particularly during the 1905 and 1917 revolutions. They played a significant role in organizing and mobilizing the peasantry against the autocratic regime of the Tsar. The party's ideology combined elements of Marxism and populism, emphasizing the importance of the peasantry as a revolutionary force.

During the Russian Revolution of 1917, the SRP initially supported the Provisional Government, which was formed after the abdication of Tsar Nicholas II. However, they later became critical of the government's policies and joined the opposition, eventually participating in the Bolshevik-led October Revolution.

Despite their initial cooperation with the Bolsheviks, the SRP soon became disillusioned with their policies, particularly regarding land redistribution. The Bolsheviks implemented a policy of collectivization, which was at odds with the SRP's emphasis on peasant ownership of land. As a result, the party was marginalized and suppressed by the Bolshevik regime.

In conclusion, the Socialist Revolutionary Party fought for peasants' rights in Russia. They advocated for land reform and the redistribution of land to the peasantry. The party played a significant role in the revolutionary movements in Russia and supported the overthrow of the Tsarist regime. However, their influence waned after the Bolsheviks came to power, as they disagreed with the Bolsheviks' policies on land and collectivization.