Lenin's conclusion that socialism may win first in one country or several countries is based on the law of unbalanced development of capitalism in the imperialist era.

Unbalanced economic and political development is the absolute law of capitalism, from which it can be concluded that socialism may win first in a few or even a single capitalist country.

-Excerpt from Lenin's Slogan on the European Federation.

The development of capitalism in various countries is extremely unbalanced, especially under the conditions of commodity production. From this, we can draw an unshakable conclusion: socialism cannot win in all countries at the same time. It will first win in one or several countries, while the rest will maintain the status of bourgeois or former bourgeois countries for a period of time.

-Excerpt from Lenin's Military Program of the Proletarian Revolution

The law of unbalanced economic and political development of imperialism is the scientific basis for the first victory of socialism in one country or several countries. Lenin pointed out that the imbalance between economic and political development is a law of capitalism, and this imbalance will be further aggravated in the era of imperialism. During the First World War, Russia became a weak link in the imperialist system. The Bolshevik Party headed by Lenin took advantage of the revolutionary situation brought by the war to Russia, led the Russian people to win the October socialist revolution, and proved Lenin's concept of one country socialism.