Explaining a Quote From “Socialism and War” by Lenin

Explain and provide background to the quote from “Socialism and War” by Lenin.

The quote is presented below:

“…socialists cannot achieve their great aim without fighting against all oppression of nations. Therefore, they must without fail demand that the Social-Democratic parties of oppressing countries (especially of the so-called “great” powers) should recognize and champion the right of oppressed nations to self-determination, precisely in the political sense of the term, i.e., the right to political secession.”