Stalin never promoted the ideology of 'socialism in one country' to mean that socialism would only be created in one country and that each revolutionary struggle would be disunified; the working class struggles being inconsistent with eachother. There's no source to support such a claim. Stalin and Lenin both realized that, contrary to Marx's theory, socialism would not take hold in industrialized nations and spread from nation to nation at the same general time. Revolutionary struggles, as history has shown us, vary based on national characteristics and the general ripeness and organization of the working class to forge revolution.
Socialism in one country does not mean that a socialist state would be isolated from other international revolutions. To the contrary, it means that each socialist country must develop and industrialize as if it would be the only socialist revolution. A nation must be prepared to defend itself from reactionary counterrevolution, as well as imperialism that attempts to undermine the struggle in favor of corporate and bourgeois interests. All workers struggles are united, but each struggle is unique based on industrial development and the preparation of the revolutionary vanguard.
A modern example would be Cuba. Cuba is not isolated from revolutionary struggle, as it collaborated with the Soviet Union and the People's Republic of China to maintain the workers state. Regardless, due to revisionism in China and the collapse of the Soviet Union, Cuba is currently left to fend mostly for itself; standing defiantly in the face of the United States' military threats and imperialist exploitation. Fidel Castro, a supporter and advocate of Marxism-Leninism, did not attempt to seclude Cuba from other socialist nations, but instead, united with them and prepared Cuba for a time in the future in which it may need to swim on its own. That time has come and thanks to the proper ideological application of socialism in one country, Cuba manages to maintain universal healthcare, education for all, housing for all its citizens and proper food and water distribution. Had Cuba not worked towards inner strength, it would be rational to say that the island would have embraced revisionist policies and likely fallen back into the hands of Western colonial states; forced under the hand of bourgeois democracy and manipulation.
As I have said, all workers struggles must unite, regardless of borders. Regardless, each workers state must properly industrialize and maintain its strength, for revolutions are not fool-proof. Revisionism has brought down many revolutions that have been ignited by the working class, but the proper application of Marxism-Leninism can secure that socialism will thrive and continue, whether united with other nations or forced into isolation. One must not misread Stalin and Lenin's statements, as both of them rationally explain why socialism must spread to bring about world revolution, but we realize that the world is not surreal. Revolutions do not happen at the same time and often times, revisionism will bring economic turbulence or a rift between socialist states. Only through internal strengthening of the workers state can revolution hope to flourish.